Theme: Pharmaceutical analysis of amino aromatic carboxylic acids and their derivatives, derivatives of acetanilide as drug substances: synthesis, properties, analysis, storage, action and use.

p-Aminobenzoic acid derivatives

Like amino acids of a fatty series, aminoaromatic acids have amphoteric character, but presence of an aromatic ring leads to prevalence of acid properties.

The most simple representative aminoaromatic acids – p-aminobenzoic acid (PABA)

In 1940 it has been enlisted to vitamins (vitamin Н₁). It is not only the vital factor for many microorganisms, but also a necessary element for biosynthesis of some vitamins of group of folic acid.

Esters of PABA shows local anesthetic effect and became synthetic substitutes of the first anesthetic cocaine (alkaloid, which is obtained from plant Erythroxylon Coca, that grows in South America). Studying of structure of cocaine and products of its disintegration has shown, that anesthetic effect is caused by presence anesthesiophoric grouping:

containing the rest of benzoic acid, which esterified by organic base, containing nitrogen. Such grouping is available in molecules of procaine hydrochloride, tetracaine hydrochloride, etc.

Local anesthesia may be defined as the loss of sensation or the loss of motor function in a circumscribed area of the body. Local anesthetics are drugs that produce this conditions by applied locally to the nerve tissue in appropriate concentrations. To be useful clinically, the action should always be reversible. The local anesthetic agents are useful chemical tools for the temporary relief of localized pain in dentistry and minor surgical procedures, as well as for producing a state of nonresistance (e.g., spinal anesthesia) without general anesthesia.

The origin of the modern local anesthetic agents can be traced to the independent discoveries of two distinctly different alkaloids, cocaine and isogramine. Cocaine is an aminoalkyl ester of benzoic acid; isogramine is a 2-(aminialkyl)indole. Insufficient data are available to make definitive statements about the relationship of the common structural features of the two molecules to local anesthetic activity.

Lidocaine derivatives are essentially anilide progenies of isogramine with the following general structural characteristics:

The benzoic acid derivatives are synthetic compounds derived from the structure of cocaine and may be represented as follows:

The clinically useful members of this series possess as aryl radical attached directly to the carbonyl group or attached through a vinyl group. Although alicyclic and aryl aliphatic carboxylic acid esters are active, conjugation of the aromatic group with the carbonyl enhances local anesthetic activity. Substitution of the aryl group with the substituents that increase the electron density of the carbonyl oxygen enhance activity. The brige X may be carbon, oxygen, nitrogen, or sulfur. In a isomeric procaine series, conduction-anesthetic potency decreased in the following order: sulfur, oxygen, carbon, nitrogen. The aminoalkyl group is not necessary for local anesthetic activity, but it is used to form water-soluble salts.

Esters of p-aminobenzoic acid

General Notices

(Ph Eur monograph 0011) Benzocaine

Anaesthesinum

Aethylis аminobenzoas*

Benzocaine

Еthyl аminobenzoate

C₉H₁₁NO₂

М m. = 165,19 g/mol

The chemical name: ethyl ester of p-aminobenzoic acid; ethyl-p-aminobenzoate.

DEFINITION

Benzocaine contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of ethyl 4-aminobenzoate, calculated with reference to the dried substance.

The first time it is synthesised in 1830, and in medicine as drug apply since 1902.

Obtaining

Initial raw materials is toluene С₆H₅СH₃ , which nitrations by means of mix nitric HNO₃ and sulphatic H₂SO₄ acids, then to oxidize methyl group –СН₃ to carboxylic –СООН by means of chromic mix (solution K₂Cr₂O₇ in H₂SO₄), to esterify by ethanol С₂Н₅ОН and reduce nitrogroup–NO₂ to an amino group–NH₂ by means of iron at presence of acetic acid СН₃СООН:

Toluene p-nitrotoluene p-nitrobenzoic acid

benzocaine

The received product clear recrystallization from the diluted alcohol with the activated coal and sodium hydrogensulphite NaHSO_{3, to} decolour the soluble painted impurity by reduction.

CHARACTERS

A white, crystalline powder or colourless crystals, very slightly soluble in water, freely soluble in alcohol.

IDENTIFICATION

First identification A, B.

Second identification A, C, D.

 A. Melting point (2.2.14): 89 °C to 92 °C.

 B. Examine by infrared absorption spectrophotometry (2.2.24), comparing with the spectrum obtained with benzocaine CRS.

 C. To about 50 mg in a test-tube add 0.2 ml of a 500 g/l solution of chromium trioxide R. Cover the mouth of the tube with a piece of filter paper moistened with a freshly prepared mixture of equal volumes of a 50 g/l solution of sodium nitroprusside R and a 200 g/l solution of piperazine hydrate R. Boil gently for at least 30 s. A blue colour develops on the filter paper.

 D. Dissolve about 50 mg in alcohol R and dilute to 100 ml with the same solvent. 2 ml of the solution gives the reaction of primary aromatic amines (2.3.1).

1. Reaction of primary aromatic amino group (SPU) (diazotization with the next azocoupling).

Some crystals of test substance dissolve in 2 ml of water R, acidify of HCl R, add 0,2 ml of sodium nitrite solution R NaNO₂ and through 1–2 mines add 1 ml of alkaline solutionb-naphthol; there is an intensive orange or red colouring and, as a rule, the precipitate of the same colour is formed.

salt diazonium azo dye of red colour

2. Lignin test (of aromatic amino group, spend reaction to a newsprint!). On a newsprint slice to put some crystals of substance and to moisten with solution HCl; there is a yellow stain, which becomes in due course orange.

The newsprint contains lignin, in which there are aromatic aldehydes. At interaction with aromatic amines are formed azomethine dye (Schiff base) orange colour:

orange

Other reactions (SPU):

1. Alkaline hydrolysis with the next revealing of ethanol С₂H₅OH with the help iodoform test (of ester group).

Drug heat up with solution of sodium hydroxide NaOH and add solution of iodine І₂ before not disappearing yellow colouring; there is iodoform smell СНІ₃.

C₂H₅OH + 4I₂ + 6NaOH → CHI₃ ↓ + 5NaI + HCOONa + 5H₂O

iodoform smell

2. Hydroxamic reaction (of ester group).

At alkaline hydrolysis of esters at presence hydroxylamine NH₂OH are formed hydroxamic acids, which with salts of heavy metals (it is the most often Iron (ІІІ)) form the salts painted in red colour – hydroxamates:

red

4. Oxidation of drug by means of chloramine at presence of chloride acid HCl leads to formation of reaction product, which at churning (shake up) with ether paints ether layer in orange colour.

TESTS

Appearance of solution

Dissolve 1.0 g in alcohol R and dilute to 20 ml with the same solvent. The solution is clear (2.2.1) and colourless (2.2.2, Method II).

Acidity or alkalinity

Dissolve 0.5 g in 10 ml of alcohol R previously neutralised to 0.05 ml of phenolphthalein solution R. Add 10 ml of carbon dioxide-free water R. The solution remains colourless and not more than 0.5 ml of 0.01 M sodium hydroxide is required to change the colour of the indicator.

Loss on drying (2.2.32)

Not more than 0.5 per cent, determined on 1.00 g by drying in vacuo.

Sulphated ash (2.4.14)

Not more than 0.1 per cent, determined on 1.0 g.

ASSAY

Nitritometry, direct titration

Dissolve 0.400 g in a mixture of 25 ml of hydrochloric acid R and 50 ml of water R, add 3 g of potassium bromide R. Cool in ice-water and titrate by slowly adding 0.1 M sodium nitrite with constant stirring.

Determine the end-point electrometrically or by the use of the prescribed indicator:

internal indicators: tropeolin 00 – before yellow colouring, a mix tropeolin 00 and methylen dark blue – transition of red-violet colouring to blue, neutral red – before dark blue colouring or

external indicators: potassium iodide test paper – before dark blue colouring.

In parallel spend control experience.

Carry out the determination of primary aromatic amino-nitrogen (2.5.8):

1) Diazotization of free aromatic amino group:

2) The excess drop of titrant NaNO₂ reacts with КI of potassium iodide test paper in the medium of HCl with formation of iodine I₂ and consequently potassium iodide test paper becomes blue.

T

2NaNO₂ + 2KI + 4HCl à I₂ + 2NO + 2KCl + 2NaCl + 2H₂O

excess drop

Е_m (C₉H₁₁NO₂) = М. м.

1 ml of 0.1 M sodium nitrite is equivalent to 16.52 mg of C₉H₁₁NO₂.

STORAGE

Store protected from light.

Action and use

Local anaesthetic.

Ph Eur

Procaine hydrochloride (Novocaine)

(Ph Eur monograph 0050)

Procaini hydrochloridum

Novocainum (N)

Aethocain

Allocaine

C₁₃H₂₀N₂O₂,HCl or C₁₃H₂₁ClN₂O₂   

М m. = 272,8 g/mol

The chemical name: 2-(diethylamino)ethyl 4-aminobenzoate hydrochloride or b-2-diethylaminoethylester of p-aminobenzoic acid hydrochloride.

DEFINITION

Procaine hydrochloride contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of 2-(diethylamino)ethyl 4-aminobenzoate hydrochloride, calculated with reference to the dried substance.

It is synthesised in 1904.

Reception

1. From benzocaine by means of alcoholysis reaction with b-diethylaminoethanol in the presence of sodium alcoholate: at interaction esters with alcohols occurs retherification (interesterification) – an exchange alcoholic rests).

novocaine-basis

Formed ethanol С₂Н₅ОН is easily driven away, as its temperature of boiling is considerable below boiling temperature diethylaminiethanol.

The obtained basis of novocaine transfer in salt action of the calculated quantity alcoholic solution of HCl:

2. From p-nitrotoluene reaction of oxidation to p-nitrobenzoic acid with the next condensation its acid chloride (SOCl₂ – thionyl chloride) with b-diethylaminoethanol and nitrogroup reduction.

Diethylaminoethanol obtained by condensation ethylene oxide with diethylamine in alcoholic solution (see tetracaine hydrochloride). For this purpose gas ethylene oxide pass throught solution diethylamine in methanol.

CHARACTERS

A white, crystalline powder or colourless crystals, very soluble in water, soluble in alcohol.

IDENTIFICATION

First identification A, B, E.

Second identification A, C, D, E, F.

 A. Melting point (2.2.14): 154 °C to 158 °C.

 B. Examine by infrared absorption spectrophotometry (2.2.24), comparing with the spectrum obtained with procaine hydrochloride CRS.

 C. To about 5 mg add 0.5 ml of fuming nitric acid R. Evaporate to dryness on a water-bath, allow to cool and dissolve the residue in 5 ml of acetone R. Add 1 ml of 0.1 M alcoholic potassium hydroxide. Only a brownish-red colour develops.

 D. To 0.2 ml of solution S (see Tests) add 2 ml of water R and 0.5 ml of dilute sulphuric acid R and shake. Add 1 ml of a 1 g/l solution of potassium permanganate R. The colour is immediately discharged.

 E. It gives reaction (a) of chlorides (2.3.1)

AgNO₃ + Procaine×HCl = AgCl↓ + Procaine×HNO₃

AgCl + 2NH₄OH = [Ag(NH₃)₂]Cl + 2H₂O

 F. Dilute 1 ml of solution S to 100 ml with water R. 2 ml of this solution gives the reaction of primary aromatic amines (2.3.1):

Reaction of primary aromatic amino group (diazotization with the next azocoupling).

Some crystals of test substance dissolve in 2 ml of water R, acidify of HCl R, add 0,2 ml of sodium nitrite solution R NaNO₂ and through 1–2 mines add 1 ml of alkaline solutionb-naphthol; there is an intensive orange or red colouring and, as a rule, the precipitate of the same colour is formed.

salt diazonium azo dye of red colour

Other reactions of identification:

1. Hydroxamic reaction (see benzocaine, reaction 3).

2. Reaction with perhydrol. To solution of novocaine add perhydrol (30 % solution hydrogen peroxide Н₂О₂) and concentrated sulphatic acid H₂SO₄; gradually there is a lilac colouring.

3. Precipitation of procaine-base. To solution of procaine hydrochloride add solution NaOH; the oily liquid (prokain-basis) is formed:

Procaine×HCl + NaOH = Prokain-base¯ + NaCl + H₂O

4. Reaction with bromic water (for aromatic ring). To solution of procaine hydrochloride add bromic water Br₂; the precipitate of dibromderivative is formed:

precipitate of dibromderivative

TESTS

Solution S

Dissolve 2.5 g in carbon dioxide-free water R and dilute to 50 ml with the same solvent.

Appearance of solution

Solution S is clear (2.2.1) and colourless (2.2.2, Method II).

pH (2.2.3)

Dilute 4 ml of solution S to 10 ml with carbon dioxide-free water R. The pH of the solution is 5.0 to 6.5.

Related substances

Examine by thin-layer chromatography (2.2.27), using silica gel GF₂₅₄ R as the coating substance.

Test solution Dissolve 1.0 g of the substance to be examined in water R and dilute to 10 ml with the same solvent.

Reference solution Dissolve 50 mg of 4-aminobenzoic acid R in water R and dilute to 100 ml with the same solvent. Dilute 1 ml of the solution to 10 ml with water R.

Apply separately to the plate 5 µl of each solution. Develop over a path of 10 cm using a mixture of 4 volumes of glacial acetic acid R, 16 volumes of hexane R and 80 volumes of dibutyl ether R. Dry the plate at 100 °C to 105 °C for 10 min and examine in ultraviolet light at 254 nm. Any spot in the chromatogram obtained with the test solution, apart from the principal spot, is not more intense than the spot in the chromatogram obtained with the reference solution (0.05 per cent). The principal spot in the chromatogram obtained with the test solution remains on the starting point.

Heavy metals (2.4.8)

Dissolve 1.0 g in water R and dilute to 25.0 ml with the same solvent. Carry out the prefiltration. 10 ml of the prefiltrate complies with limit test E for heavy metals (5 ppm). Prepare the standard using 2 ml of lead standard solution (1 ppm Pb) R.

Loss on drying (2.2.32)

Not more than 0.5 per cent, determined on 1.00 g by drying in an oven at 100 °C to 105 °C.

Sulphated ash (2.4.14)

Not more than 0.1 per cent, determined on 1.0 g.

ASSAY

Nitritometry, direct titration

Dissolve 0.400 g in 50 ml of dilute hydrochloric acid R. add water R, add 3 g of potassium bromide R. Cool in ice-water and titrate by slowly adding 0.1 M sodium nitrite with constant stirring with indicator (SPU: mix tropeolin 00 (4 drops) and methylen dark blue (2 drops)– transition of red-violet colouring to blue) until blue colour.

Carry out the determination of primary aromatic amino-nitrogen (2.5.8):

1) Diazotization of free aromatic amino group:

2) The excess drop of titrant NaNO₂ reacts with КI of potassium iodide test paper in the medium of HCl with formation of iodine I₂ and consequently potassium iodide test paper becomes blue.

T

2NaNO₂ + 2KI + 4HCl à I₂ + 2NO + 2KCl + 2NaCl + 2H₂O

excess drop

Е_m(C₁₃H₂₁ClN₂O₂) = М. м.

1 ml of 0.1 M sodium nitrite is equivalent to 27.28 mg of C₁₃H₂₁ClN₂O₂.

STORAGE

Store protected from light.

Action and use

Local anaesthetic.

Ph Eur

Tetracaine hydroсhloride

(Ph Eur monograph 0057)

NOTE: The name Amethocaine Hydrochloride was formerly used in the United Kingdom.

Dicainum

Tetracaini hydroсhloridum

C₁₅H₂₄N₂O₂,HCl

М m. = 300,83 g/mol

The chemical name: β-Dimethylaminoethylester of p-butylaminobenzoic acid hydrochloride.

DEFINITION

Tetracaine hydrochloride contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of 2-(dimethylamino)ethyl 4-(butylamino)benzoate hydrochloride, calculated with reference to the dried substance.

Obtaining

Initial substances for synthesis tetracaine hydrochloride is p-aminobenzoic acid (its synthesis from toluene – see benzocaine) and dimethylaminoethanol, which obtained by condensation ethylene oxide with dimethylamine in the medium of alcohol:

Tetracaine hydrochloride obtained under such scheme: p-aminobenzoic acid heat up in the alkaline medium with p-butylbromide and obtained p-butylaminobenzoic acid by interaction with thionyl chloride SOCl₂ transform in acid chloride, which condense with β-dimehylaminoethanol.

CHARACTERS

A white, crystalline powder, slightly hygroscopic, freely soluble in water, soluble in alcohol.

It melts at about 148 °C or it may occur in either of 2 other crystalline forms which melt respectively at about 134 °C and 139 °C. Mixtures of these forms melt within the range 134 °C to 147 °C.

IDENTIFICATION

First identification A, B, D.

Second identification B, C, D.

 A. Examine by infrared absorption spectrophotometry (2.2.24), comparing with the spectrum obtained with tetracaine hydrochloride CRS.

 B. To 10 ml of solution S (see Tests) add 1 ml of ammonium thiocyanate solution R. A white, crystalline precipitate is formed which, after recrystallisation from water R and drying at 80 °C for 2 h, melts (2.2.14) at about 131 °C.

 C. Nitration of tetracaine hydrochloride with the next formation aci-nitroform of potassium salt salts with ortho-quinoid structure. To about 5 mg add 0.5 ml of fuming nitric acid R. Evaporate to dryness on a water-bath, allow to cool and dissolve the residue in 5 ml of acetone R. Add 1 ml of 0.1 M alcoholic potassium hydroxide. A violet (SPU - or red) colour develops.

 D. Solution S gives reaction (a) of chlorides (2.3.1).

AgNO₃ + Tetracaine×HCl = AgCl↓ + Tetracaine×HNO₃

*For salts of the organic bases test of solubility of formed precipitate AgCl spend after filtration and washings of precipitate by water. AgCl + 2NH₄OH = [Ag(NH₃)₂]Cl + 2H₂O

Other peactions:

1. Reaction of secondary amino group after alkaline hydrolysis.

a) at boiling solution of test substance with solution NaOH is formed sodium salt p-butylaminobenzoic acid:

b) At acidifying hydrolysis product by chloride acid HCl the white precipitate p-butylaminobenzoic acid, which is dissolved in excess of HCl:

white precipitate

c) At action of sodium nitrite NaNO₂ in the medium of chloride acid diluted HCl precipitate of N-nitroso compound of this acid is formed:

2. Hydroxamic reaction (see benzocaine, reaction 3).

3. Unlike benzocaine and novocaine, tetracaine hydrochloride not diazotized (does not contain a free amino group–NH₂).

TESTS

Solution S

Dissolve 5.0 g in carbon dioxide-free water R and dilute to 50 ml with the same solvent.

Appearance of solution

Dilute 2 ml of solution S to 10 ml with water R. The solution is clear (2.2.1) and colourless (2.2.2, Method II).

pH (2.2.3)

Dilute 1 ml of solution S to 10 ml with carbon dioxide-free water R. The pH of the solution is 4.5 to 6.5.

Related substances

Examine by thin-layer chromatography (2.2.27), using a TLC silica gel GF₂₅₄plate R. Carry out a preliminary development over a path of 12 cm using a mixture of 4 volumes of glacial acetic acid R, 16 volumes of hexane R and 80 volumes of dibutyl ether R. Remove the plate and dry it in a current of warm air for a few minutes. Allow the plate to cool before use.

Test solution Dissolve 1.0 g of the substance to be examined in water R and dilute to 10 ml with the same solvent.

Reference solution Dissolve 50 mg of 4-aminobenzoic acid R in water R and dilute to 100 ml with the same solvent. Dilute 1 ml of the solution to 10 ml with water R.

Apply to the plate 5 µl of each solution. Develop over a path of 10 cm using a mixture of 4 volumes of glacial acetic acid R, 16 volumes of hexane R and 80 volumes of dibutyl ether R. Dry the plate at 100 °C to 105 °C for 10 min and examine in ultraviolet light at 254 nm. Any spot in the chromatogram obtained with the test solution, apart from the principal spot, is not more intense than the spot in the chromatogram obtained with the reference solution (0.05 per cent). The principal spot in the chromatogram obtained with the test solution remains at the starting point.

Heavy metals (2.4.8)

12 ml of solution S complies with limit test A for heavy metals (10 ppm). Prepare the standard using lead standard solution (1 ppm Pb) R.

Loss on drying (2.2.32)

Not more than 1.0 per cent, determined on 1.000 g by drying in an oven at 100 °C to 105 °C.

Sulphated ash (2.4.14)

Not more than 0.1 per cent, determined on 1.0 g.

ASSAY

Dissolve 0.250 g in 50 ml of alcohol R and add 5.0 ml of 0.01 M hydrochloric acid. Carry out a potentiometric titration (2.2.20), using 0.1 M sodium hydroxide. Read the volume added between the 2 points of inflexion.

1 ml of 0.1 M sodium hydroxide is equivalent to 30.08 mg of C₁₅H₂₅ClN₂O₂.

SPU. Alkalimetry (of bounded HCl). Exact volume of test solution of tetracaine hydrochloride titrate with standard solution of NaOH in the presence of chloroform (to extract the tetracaine-base) and the indicator – phenolphthalein before occurrence light-pink colou.

Tetracaine ×HCl + NaOH Д Tetracaine ×base¯ + NaCl + H₂O

Е_m (C₁₅H₂₄N₂O₂ ×HCl) = М m.

Other method of assay:

1. Nitritometry, direct titration (nitrosation of secondary amino group)

Nearby 0,3 g (exact shot) of drug dissolve in 10 ml of water and 10 ml of chloride acid diluted HCl, add dilute water to 80 ml. Add 1 g of KBr and at constant mixing (slowly!) titrate with 0,1M solution of sodium nitrite NaNO₂ at temperature not above 18–20 °C.

As the indicator it is possible to use:

Internal indicators (tropeolin 00 – titrate from red before yellow colouring; a mix tropeilin 00 and methyl dark blue – from red-violet before blue colouring; neutral red – from crimson before dark blue colouring);

The external indicator – potassium iodide test paper (titrate before occurrence of dark blue colouring).

The excess drop of titrant NaNO₂ reacts with КI of potassium iodide test paper in the medium of HCl with formation of iodine I₂ and consequently potassium iodide test paper becomes blue.

2NaNO₂ + 2KI + 4HCl ® I₂ + 2NO + 2KCl + 2NaCl + 2H₂O

STORAGE

Store protected from light.

Action and use

Local anaesthetic.

Preparation

Tetracaine Eye Drops

PROCAINAMIDE HYDROCHLORIDE

(Ph Eur monograph 0567)

Procainamidi hydrochloridum

Novocainamidum (N)

Procainamidum

Amidoprocain

C₁₃H₂₁N₃O,HCl or C₁₃H₂₂ClN₃O

М m. = 271,78 g/mol

The chemical name:4-amino-N-[2-(diethylamino)ethyl]benzamide hydrochloride or β-diethylaminoethylamide of p-aminobenzoic acid hydrochloride (SPU).

DEFINITION

Procainamide hydrochloride contains not less than 98.0 per cent and not more than the equivalent of 101.0 per cent of 4-amino-N-[2-(diethylamino)ethyl]benzamide hydrochloride, calculated with reference to the dried substance.

Obtaining (like obtaining of novocaine and benzocaine)

Initial raw materials is toluene C₆H₅CH₃ which nitration, oxidize to p-nitrobenzoic acid; acid chloride to condense with diethylaminoethylamine with the next reduction of nitrogroup and acidifying by means of chloride acid:

Procainamide hydrochloride

CHARACTERS

A white or very slightly yellow, crystalline powder, hygroscopic, very soluble in water, freely soluble in alcohol, slightly soluble in acetone.

IDENTIFICATION

First identification C, D.

Second identification A, B, D, E.

 A. Melting point (2.2.14): 166 °C to 170 °C.

 B. UV-spectroscopy of an alkaline solution. Dissolve 10.0 mg in 0.1 M sodium hydroxide and dilute to 100.0 ml with the same solvent. Dilute 10.0 ml of the solution to 100.0 ml with 0.1 M sodium hydroxide. Examined between 220 nm and 350 nm (2.2.25), the solution shows an absorption maximum at 273 nm. The specific absorbance at the maximum is 580 to 610.

 C. Examine by infrared absorption spectrophotometry (2.2.24), comparing with the spectrum obtained with procainamide hydrochloride CRS.

 D. Dilute 1 ml of solution S to 5 ml with water R. The solution gives reaction (a) of chlorides (2.3.1):

AgNO₃ + Procainamide ×HCl = AgCl↓ + Procainamide ×HNO₃

*For salts of the organic bases test of solubility of formed precipitate AgCl spend after filtration and washings of precipitate by water. AgCl + 2NH₄OH = [Ag(NH₃)₂]Cl + 2H₂O

At addition of HNO₃ white precipitate AgCl again is formed:

[Ag (NH₃) ₂] Cl + 2HNO₃ → AgCl ↓ + 2NH₄NO₃

 E. Dilute 1 ml of solution S (see Tests) to 2 ml with water R. 1 ml of this solution gives the reaction of primary aromatic amines (2.3.1).

Reaction of solution S on primary aromatic amines (SPU) (diazotization with the next azocoupling).

Some crystals of test substance dissolve in 2 ml of water R, acidify of HCl R, add 0,2 ml of sodium nitrite solution R NaNO₂ and through 1–2 mines add 1 ml of an alkaline solutionb-naphthol, there is an intensive orange or red colouring and, as a rule, the precipitate of the same colour is formed.

salt diazonium azo dye of red colour

Other reactions:

1. Hydroxamic reaction of ester group, see benzocaine, reaction 3).

2. Reaction with ammonium vanadate.

To test solution add solution of ammonium vanadate NH₄VO₃, sulphatic acid concentrated H₂SO₄ and heat up; dark red colouring (difference from novocaine) is formed.

3. Lignin test (of aromatic amino group, see benzocaine, reaction 5).

4. Reaction with bromic water (of aromatic ring). To test solution add bromic water Br₂; the precipitate of dibromoderivative is formed:

TESTS

Solution S

Dissolve 2.5 g in carbon dioxide-free water R and dilute to 25 ml with the same solvent.

Appearance of solution

Solution S is clear (2.2.1) and not more intensely coloured than reference solution B₆ (2.2.2, Method II).

pH (2.2.3)

The pH of solution S is 5.6 to 6.3.

Related substances

Examine by thin-layer chromatography (2.2.27), using silica gel GF₂₅₄ R as the coating substance.

Test solution Dissolve 0.10 g of the substance to be examined in alcohol R and dilute to 10 ml with the same solvent.

Reference solution Dilute 1 ml of the test solution to 200 ml with alcohol R.

Apply to the plate 5 µl of each solution. Develop over a path of 12 cm using a mixture of 15 volumes of glacial acetic acid R, 30 volumes of water R and 60 volumes of butanol R. Place the plate in a stream of cold air until the plate appears dry. Examine in ultraviolet light at 254 nm. Any spot in the chromatogram obtained with the test solution, apart from the principal spot, is not more intense than the spot in the chromatogram obtained with the reference solution (0.5 per cent).

Heavy metals (2.4.8)

1.0 g complies with limit test C for heavy metals (20 ppm). Prepare the standard using 2 ml of lead standard solution (10 ppm Pb) R.

Loss on drying (2.2.32)

Not more than 0.5 per cent, determined on 1.000 g by drying in an oven at 100 °C to 105 °C.

Sulphated ash (2.4.14)

Not more than 0.1 per cent, determined on 1.0 g.

ASSAY

Nitritometry, direct titration

Dissolve 0.2500 g in 50 ml of dilute hydrochloric acid R, add water R, add 3 g of potassium bromide R. Cool in ice-water and titrate by slowly adding 0.1 M sodium nitrite with constant stirring with indicator (SPU: mix tropeolin 00 (4 drops) and methylen dark blue (2 drops)– transition of red-violet colouring to blue) until blue colour.

Carry out the determination of primary aromatic amino-nitrogen (2.5.8):

1) Diazotization of free aromatic amino group:

R=NH-CH₂CH₂ N(C₂H₅)₂

2) The excess drop of titrant NaNO₂ reacts with КI of potassium iodide test paper in the medium of HCl with formation of iodine I₂ and consequently potassium iodide test paper becomes blue.

T

2NaNO₂ + 2KI + 4HCl à I₂ + 2NO + 2KCl + 2NaCl + 2H₂O

excess drop

Е_m (C₁₃H₂₂ClN₃O) = М. м.

1 ml of 0.1 M sodium nitrite is equivalent to 27.18 mg of C₁₃H₂₂ClN₃O.

STORAGE

Store in an airtight container , protected from light.

Action and use

Anti-arrhythmic.

Preparations

Procainamide Injection

Procainamide Tablets

Ph Eur

Articaine hydrochloride

Articaini hydrochloridum

Ultracainе

Химическое название: methyl ester of 4-methyl-3[2-propylaminopropionamide]-2-thiophene carboxylic acid hydrochloride.

(Ph Eur monograph 1688)

C₁₃H₂₀N₂O₃S,HCl  M.m. = 320.8 g/mol

DEFINITION

Methyl 4-methyl-3-[[(2RS)-2-(propylamino)propanoyl]amino]thiophene-2-carboxylate hydrochloride.

Content

98.5 per cent to 101.0 per cent (dried substance).

CHARACTERS

Appearance

White or almost white, crystalline powder.

Solubility

Freely soluble in water and in alcohol.

IDENTIFICATION

First identification B, D.

Second identification A, C, D.

 A. Dissolve 50.0 mg in a 1 g/l solution of hydrochloric acid R and dilute to 100.0 ml with the same acid. Dilute 5.0 ml of the solution to 100.0 ml with a 1 g/l solution of hydrochloric acid R. Examined between 200 nm and 350 nm (2.2.25), the solution shows an absorption maximum at 272 nm. The specific absorbance at the maximum is 290 to 320.

 B. Infrared absorption spectrophotometry (2.2.24).

Preparation Place dropwise 20 µl of the test solution on 300 mg discs.

Test solution Dissolve 0.1 g in 5 ml of water R, add 3 ml of a saturated solution of sodium hydrogen carbonate R and shake twice with 2 ml of methylene chloride R. Combine the methylene chloride layers, dilute to 5.0 ml with methylene chloride R and dry over anhydrous sodium sulphate R.

Comparison articaine hydrochloride CRS.

 C. Thin-layer chromatography (2.2.27).

Test solution Dissolve 20 mg of the substance to be examined in 5 ml of alcohol R.

Reference solution Dissolve 20 mg of articaine hydrochloride CRS in 5 ml of alcohol R.

Plate TLC silica gel F₂₅₄plate R.

Mobile phase triethylamine R, ethyl acetate R, heptane R (10:35:65 V/V/V).

Application 5 µl.

Development Over a path of 15 cm.

Drying In air.

Detection Examine in ultraviolet light at 254 nm.

Results The principal spot in the chromatogram obtained with the test solution is similar in position and size to the principal spot in the chromatogram obtained with the reference solution.

 D. It gives reaction (a) of chlorides (2.3.1):

AgNO₃ + Articaine ×HCl = AgCl↓ + Articaine ×HNO₃

*For salts of the organic bases test of solubility of formed precipitate AgCl spend after filtration and washings of precipitate by water. AgCl + 2NH₄OH = [Ag(NH₃)₂]Cl + 2H₂O

At addition of HNO₃ white precipitate AgCl again is formed:

[Ag (NH₃) ₂] Cl + 2HNO₃ → AgCl ↓ + 2NH₄NO₃

SPU. Other reactions of identification:

1. Drug pyrolysis (dry or damp) with the next definition ionogenic bounded of Sulfur.

a) Dry pyrolysis (substance burning) leads to formation of hydrogen sulphide H₂S, which reveal by means of darkening lead-acetic paper Pb (CH₃COO) ₂:

Pb²⁺ + S^2– ® PbS↓

dark brown or black

b) Damp pyrolysis: mineralizes of drug by action strong HNO_3, that does not contain Sulfur; thus Sulfur passes in structure of sulphate-ions SO₄^{2 -} , which reveal behind formation of a white precipitate at interaction with BaCl₂ or Ba (NO₃) ₂:

Ba^{2 +} + SO₄^{2 -} → BaSO₄ ↓

white

The precipitate is insoluble neither in acids, nor in alkalis.

2. Hydrolysis of articaine with the next identification of methanol (for ester group –COO–):

Methanol identifies after its oxidation to formaldehyde HCНО by solution of KMnО₄ in the medium of phosphatic acid H₃PO₄:

5CH₃OH + 2KMnО₄ + 3H₃PO₄ ® 5HCНО + 2MnHPO₄ + K₂HPO₄ + 8H₂O

Excess KMnО₄ through 2-3 mines decompose with the help of NaHSO₃ before solution decolouration.

Formaldehyde identifies by means of interaction with disodium salt chromotrope acid in the presence of concentrated sulphatic acid H₂SO₄; it is formed aurin dye of violet colour:

aurin dye of violet colour

3. Hydrolysis of articaine with the next identification of primary amino group R–NH₂ (of amide bound–CO–NH–)

TESTS

Solution S

Dissolve 0.50 g in water R and dilute to 10 ml with the same solvent.

Appearance of solution

Solution S is clear (2.2.1) and not more intensely coloured than reference solution BY₆ (2.2.2, Method I).

pH (2.2.3)

4.2 to 5.2.

Dissolve 0.20 g in carbon dioxide-free water R and dilute to 20.0 ml with the same solvent.

Related substances

Liquid chromatography (2.2.29).

Test solution Dissolve 10.0 mg of the substance to be examined in the mobile phase and dilute to 10.0 ml with the mobile phase.

Reference solution (a) Dilute 1.0 ml of the test solution to 100.0 ml with the mobile phase. Dilute 1.0 ml of this solution to 10.0 ml with the mobile phase.

Reference solution (b) Dissolve 10.0 mg of articaine impurity A CRS and 5.0 mg of articaine impurity E CRS in the mobile phase and dilute to 100.0 ml with the mobile phase.

Reference solution (c) Add 1.0 ml of reference solution (b) to 50.0 mg of articaine hydrochloride CRS and dilute to 50 ml with the mobile phase.

Reference solution (d) Dilute 1.0 ml of reference solution (b) to 50.0 ml with the mobile phase.

Column: 

 —size: l = 0.25 m, Ш = 4.6 mm,

 —stationary phase: spherical end-capped octadecylsilyl silica gel for chromatography R (5 µm) with a specific surface area of 335 m²/g and a carbon loading of 19 per cent,

 —temperature: 45 °C.

Mobile phase Mix 25 volumes of acetonitrile R and 75 volumes of a solution prepared as follows: dissolve 2.02 g of sodium heptanesulphonate R and 4.08 g of potassium dihydrogen phosphate R in water R and dilute to 1000 ml with the same solvent. Adjust to pH 2.0 with phosphoric acid R.

Flow rate 1 ml/min.

Detection Spectrophotometer at 276 nm.

Injection 10 µl; inject the test solution and reference solutions (a), (c) and (d).

Run time 5 times the retention time of articaine.

Relative retentions with reference to articaine (retention time = about 9.3 min): impurity B = about 0.6; impurity D = about 0.7; impurity A = about 0.8; impurity E = about 0.86; impurity F = about 0.9; impurity G = about 1.7; impurity H = about 2.1; impurity I = about 2.6; impurity C = about 3.6; impurity J = about 4.0.

System suitability Reference solution (c):

 —resolution: minimum 1.2 between the peaks due to impurity A and impurity E.

Limits:

 —impurity A: not more than the area of the corresponding peak in the chromatogram obtained with reference solution (d) (0.2 per cent),

 —any other impurity: not more than the area of the principal peak in the chromatogram obtained with reference solution (a) (0.1 per cent),

 —total of other impurities: not more than 5 times the area of the principal peak in the chromatogram obtained with reference solution (a) (0.5 per cent),

 —disregard limit: half the area of the principal peak in the chromatogram obtained with reference solution (a) (0.05 per cent).

Heavy metals (2.4.8)

Maximum 5 ppm.

Dissolve 4.0 g in 20.0 ml of water R. 12 ml of the solution complies with limit test A. Prepare the standard using lead standard solution (1 ppm Pb) R.

Loss on drying (2.2.32)

Maximum 0.5 per cent, determined on 1.000 g by drying in an oven at 100-105 °C for 5 h.

Sulphated ash (2.4.14)

Maximum 0.1 per cent, determined on 1.0 g.

IMPURITIES

Specified impurities  A, B, C.

Other detectable impurities D, E, F, G, H, I, J.

 A. R = CH₃, R = H: methyl 3-[[2-(propylamino)acetyl]amino]-4-methylthiophene-2-carboxylate (acetamidoarticaine),

 B. R = H, R = CH₃: 4-methyl-3-[[(2RS)-2-(propylamino)propanoyl]amino]thiophene-2-carboxylic acid (articaine acid),

 C. R = CH(CH₃)₂, R = CH₃: 1-methylethyl 4-methyl-3-[[(2RS)-2-(propylamino)propanoyl]amino]thiophene-2-carboxylate (articaine isopropyl ester),

 D. R1 = CH₂-CH₃, R2 = H, R3 = OCH₃: methyl 3-[[(2RS)-2-(ethylamino)propanoyl]amino]-4-methylthiophene-2-carboxylate (ethylarticaine),

 E. R1 = CH(CH₃)₂, R2 = H, R3 = OCH₃: methyl 4-methyl-3-[[(2RS)-2-[(1-methylethyl)amino]propanoyl]amino]thiophene-2-carboxylate (isopropylarticaine),

 F. R1 = CH₂-CH₂-CH₃, R2 = H, R3 = NH-CH₂-CH₂-CH₃: 4-methyl-N-propyl-3-[[(2RS)-2-(propylamino)propanoyl]amino]thiophene-2-carboxamide (articaine acid propionamide),

 G. R1 = (CH₂)₃-CH₃, R2 = H, R3 = OCH₃: methyl 3-[[(2RS)-2-(butylamino)propanoyl]amino]-4-methylthiophene-2-carboxylate (butylarticaine),

 H. R1 = R2 = CH₂-CH₂-CH₃, R3 = OCH₃: methyl 3-[[(2RS)-2-(dipropylamino)propanoyl]amino]-4-methylthiophene-2-carboxylate (dipropylarticaine),

 I. methyl 3-amino-4-methylthiophene-2-carboxylate (3-aminoarticaine),

 J. methyl 3-[[(2RS)-2-bromopropanoyl]amino]-4-methylthiophene-2-carboxylate (bromo compound).

Ph Eur

ASSAY

Dissolve 0.250 g in a mixture of 5.0 ml of 0.01 M hydrochloric acid and 50 ml of alcohol R. Carry out a potentiometric titration (2.2.20) using 0.1 M sodium hydroxide. Read the volume added between the 2 points of inflexion.

1 ml of 0.1 M sodium hydroxide is equivalent to 32.08 mg of C₁₃H₂₁ClN₂O₃S.

Other metods of assay (SPU):

1. Argentometry (for bounded HCl)

Volhard method, back titration. To investigated solution add double excess of standard solution of AgNO₃. Excess of AgNO₃ titrate with standard solution of NH₄SCN in the presence of ammonium iron alum (NH₄) Fe (SO₄) ₂ as indicator before red-pink colouring.

R×HCl + AgNO₃ ®R×HNO₃ + AgCl ↓

AgNO₃ + NH₄SCN = AgSCN¯ + NH₄NO₃

3NH₄SCN + (NH₄) Fe (SO₄) ₂ = Fe (SCN) ₃ + 2 (NH₄) ₂SO₄

red-pink

Е_m = М m.

2. Аlkalimetry (for bounded HCl) in the medium of organic solvent.

Exact volume of articaine test solution titrate with standard solution of NaOH in the presence of organic solvent (e.g. chloroform) (for infusion of articaine-base) and the indicator – phenolphthalein before occurrence light-pink colouring.

Articaine×HCl + NaOH = Articaine ×base¯ + NaCl + H₂O

Е_m = М m.

STORAGE

Protected from light.

Action and use

Local anaesthetic.

Ph Eur

Derivatives arylaliphatic acids as drugs

To this group of druds concerns ibuprofen – 2-phenylpropionic acid derivative.

Ibuprofen

Ibuprofenum

General Notices

(Ph Eur monograph 0721)

C₁₃H₁₈O₂  M.m. = 206.3  

DEFINITION

(2RS)-2-[4-(2-Methylpropyl)phenyl]propanoic acid.

Content

98.5 per cent to 101.0 per cent (dried substance).

CHARACTERS

Appearance

White, crystalline powder or colourless crystals.

Solubility

Practically insoluble in water, freely soluble in acetone, in methanol and in methylene chloride. It dissolves in dilute solutions of alkali hydroxides and carbonates.

IDENTIFICATION

First identification A, C.

Second identification A, B, D.

 A. Melting point (2.2.14): 75 °C to 78 °C.

 B. UV-spectroscopy. Dissolve 50.0 mg in a 4 g/l solution of sodium hydroxide R and dilute to 100.0 ml with the same alkaline solution. Examined between 240 nm and 300 nm (2.2.25), using a spectrophotometer with a band width of 1.0 nm and a scan speed of not more than 50 nm/min, the solution shows a shoulder at 258 nm and 2 absorption maxima, at 264 nm and 272 nm. The ratio of the absorbance measured at the maximum at 264 nm to that measured at the shoulder at 258 nm is 1.20 to 1.30. The ratio of the absorbance measured at the maximum at 272 nm to that measured at the shoulder at 258 nm is 1.00 to 1.10.

 C. Infrared absorption spectrophotometry (2.2.24).

Preparation Discs.

Comparison ibuprofen CRS.

 D. Thin-layer chromatography (2.2.27).

Test solution Dissolve 50 mg of the substance to be examined in methylene chloride R and dilute to 10 ml with the same solvent.

Reference solution Dissolve 50 mg of ibuprofen CRS in methylene chloride R and dilute to 10 ml with the same solvent.

Plate TLC silica gel plate R.

Mobile phase anhydrous acetic acid R, ethyl acetate R, hexane R (5:24:71 V/V/V).

Application 5 µl.

Development Over a path of 10 cm.

Drying At 120 °C for 30 min.

Detection Lightly spray with a 10 g/l solution of potassium permanganate R in dilute sulphuric acid R and heat at 120 °C for 20 min. Examine in ultraviolet light at 365 nm.

Results The principal spot in the chromatogram obtained with the test solution is similar in position, colour and size to the principal spot in the chromatogram obtained with the reference solution.

TESTS

Solution S

Dissolve 2.0 g in methanol R and dilute to 20 ml with the same solvent.

Appearance of solution

Solution S is clear (2.2.1) and colourless (2.2.2, Method II).

Angle of optical rotation (2.2.7)

- 0.05° to + 0.05°.

Dissolve 0.50 g in methanol R and dilute to 20.0 ml with the same solvent.

Related substances

Liquid chromatography (2.2.29).

Test solution Dissolve 20 mg of the substance to be examined in 2 ml of acetonitrile R and dilute to 10.0 ml with mobile phase A.

Reference solution (a) Dilute 1.0 ml of the test solution to 100.0 ml with mobile phase A.

Reference solution (b) Dissolve 20 mg of ibuprofen CRS in 2 ml of acetonitrile R, add 1.0 ml of a 0.06 g/l solution of ibuprofen impurity B CRS in acetonitrile R and dilute to 10.0 ml with mobile phase A.

Column: 

 —size: l = 0.15 m, Ш = 4.6 mm,

 —stationary phase: octadecylsilyl silica gel for chromatography R (5 µm).

Mobile phase:

 —mobile phase A: mix 0.5 volumes of phosphoric acid R, 340 volumes of acetonitrile R and 600 volumes of water R; allow to equilibrate and dilute to 1000 volumes with water R,

 —mobile phase B: acetonitrile R,

Flow rate 2 ml/min.

Detection Spectrophotometer at 214 nm.

Equilibration For about 45 min with mobile phase A.

Injection 20 µl.

System suitability Reference solution (b):

 —peak-to-valley ratio: minimum of 1.5, where H_p = height above the baseline of the peak due to impurity B, and H_v = height above the baseline of the lowest point of the curve separating this peak from the peak due to ibuprofen. If necessary, adjust the concentration of acetonitrile in mobile phase A.

Limits:

 —impurity B: not more than the area of the corresponding peak in the chromatogram obtained with reference solution (b) (0.3 per cent),

 —any other impurity: not more than 0.3 times the area of the principal peak in the chromatogram obtained with reference solution (a) (0.3 per cent),

 —total of all impurities apart from impurity B: not more than 0.7 times the area of the principal peak in the chromatogram obtained with reference solution (a) (0.7 per cent),

 —disregard limit: 0.05 times the area of the principal peak in the chromatogram obtained with reference solution (a) (0.05 per cent).

Impurity F

Gas chromatography (2.2.28): use the normalisation procedure.

Methylating solution Dilute 1 ml of N,N-dimethylformamide dimethyl acetal R and 1 ml of pyridine R to 10 ml with ethyl acetate R.

Test solution Weigh about 50.0 mg of the substance to be examined into a sealable vial, dissolve in 1.0 ml of ethyl acetate R, add 1 ml of methylating solution, seal and heat at 100 °C in a block heater for 20 min. Allow to cool. Remove the reagents under a stream of nitrogen at room temperature. Dissolve the residue in 5 ml of ethyl acetate R.

Reference solution (a) Dissolve 0.5 mg of ibuprofen impurity F CRS in ethyl acetate R and dilute to 10.0 ml with the same solvent.

Reference solution (b) Weigh about 50.0 mg of ibuprofen CRS into a sealable vial, dissolve in 1.0 ml of reference solution (a), add 1 ml of methylating solution, seal and heat at 100 °C in a block heater for 20 min. Allow to cool. Remove the reagents under a stream of nitrogen at room temperature. Dissolve the residue in 5 ml of ethyl acetate R.

Column: 

 —material: fused-silica,

 —size: l = 25 m, Ш = 0.53 mm,

 —stationary phase: macrogol 20 000 R (film thickness 2 µm).

Carrier gas helium for chromatography R.

Flow rate 5.0 ml/min.

Temperature:

 —column: 150 °C,

 —injection port: 200 °C,

 —detector: 250 °C.

Detection Flame-ionisation.

Injection 1 µl; inject the test solution and reference solution (b).

Run time Twice the retention time of ibuprofen.

System suitability:

 —relative retention with reference to ibuprofen (retention time = about 17 min): impurity F = about 1.5.

Limit:

 —impurity F: maximum 0.1 per cent.

Heavy metals (2.4.8)

Maximum 10 ppm.

12 ml of solution S complies with limit test B. Prepare the standard using lead standard solution (1 ppm Pb) prepared by diluting lead standard solution (100 ppm Pb) R with methanol R.

Loss on drying (2.2.32)

Maximum 0.5 per cent, determined on 1.000 g by drying in vacuo over diphosphorus pentoxide R.

Sulphated ash (2.4.14)

Maximum 0.1 per cent, determined on 1.0 g.

IMPURITIES

Specified impurities A, B, C, D, E.

Other detectable impurities F, G, H, I, J, K, L, M, N, O, P, Q, R.

 A. R1 = OH, R2 = CH₂-CH(CH₃)₂, R3 = H: (2RS)-2-[3-(2-methylpropyl)phenyl]propanoic acid,

 B. R1 = OH, R2 = H, R3 = [CH₂]₃-CH₃: (2RS)-2-(4-butylphenyl)propanoic acid,

 C. R1 = NH₂, R2 = H, R3 = CH₂-CH(CH₃)₂: (2RS)-2-[4-(2-methylpropyl)phenyl]propanamide,

 D. R1 = OH, R2 = H, R3 = CH₃: (2RS)-2-(4-methylphenyl)propanoic acid,

E. 1-[4-(2-methylpropyl)phenyl]ethanone, 

 F. 3-[4-(2-methylpropyl)phenyl]propanoic acid,

 G. cis-7-(2-methylpropyl)-1-[4-(2-methylpropyl)phenyl]-1,2,3,4-tetrahydronaphthalene-1,4-dicarboxylic acid,

 H. X = O: (3RS)-1,3-bis[4-(2-methylpropyl)phenyl]butan-1-one,

 I. X = H₂: (3RS)-1,3-bis[4-(2-methylpropyl)phenyl]butane,

 J. R = H, R4 = CO-CH(CH₃)₂: (2RS)-2-[4-(2-methylpropanoyl)phenyl]propanoic acid,

 K. R = H, R4 = CHO: (2RS)-2-(4-formylphenyl)propanoic acid,

 L. R = H, R4 = CHOH-CH(CH₃)₂: 2-[4-(1-hydroxy-2-methylpropyl)phenyl]propanoic acid,

 M. R = OH, R4 = CH₂-CH(CH₃)₂: (2RS)-2-hydroxy-2-[4-(2-methylpropyl)phenyl]propanoic acid,

 N. R = H, R4 = C₂H₅: (2RS)-2-(4-ethylphenyl)propanoic acid,

 O. R = H, R4 = CH(CH₃)-C₂H₅: 2-[4-(1-methylpropyl)phenyl]propanoic acid,

 P. R = CH₃: (2RS)-2-[4-(2-methylpropyl)phenyl]propan-1-ol,

 Q. R = H: 2-[4-(2-methylpropyl)phenyl]ethanol,

 R. 1,1-bis[4-(2-methylpropyl)phenyl]ethane.

Ph Eur

ASSAY

Alkalimetry of methanol solution, direct titration

Dissolve 0.450 g in 50 ml of methanol R. Add 0.4 ml of phenolphthalein solution R1. Titrate with 0.1 M sodium hydroxide until a red colour is obtained. Carry out a blank titration.

Е_m (C₁₃H₁₈O₂) = М m.

1 ml of 0.1 M sodium hydroxide is equivalent to 20.63 mg of C₁₃H₁₈O₂.

Storage

The list of strong substances. In the air-tight container, in the place protected from light.

Action and use

Anti-inflammatory; analgesic.

Preparations

Ibuprofen Cream

Ibuprofen Gel

Ibuprofen Oral Suspension

Ibuprofen Tablets

Ph Eur

Derivatives of acetanilide

To derivatives of acetanilide С₆Н₅–NH–CO–CH₃, containing diethyl aminogen group –N (C₂H₅) _2, which causes local anesthetic effect, drugs – lidocaine and trimecaine hydrochloride concern.

Lidocaine (in Ukraine)

Lidocainum

Xycainum

Xylocainum

С₁₄Н₂₂N₂O×HCl М m. = 270,79 g/mol

The chemical name: 2-diethylamino-2,6-dimethylacetanilide hydrochloride

(Ph Eur monograph 0727) Lidocaine

NOTE: The name Lignocaine was formerly used in the United Kingdom.

Preparation Lidocaine Ointment

C₁₄H₂₂N₂O   M.m. = 234.3 g/mol 

DEFINITION

Lidocaine contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide, calculated with reference to the anhydrous substance.

CHARACTERS

A white or almost white, crystalline powder, practically insoluble in water, very soluble in alcohol and in methylene chloride.

(Ph Eur monograph 0227) Lidocaine hydrochloride

NOTE: The name Lignocaine Hydrochloride was formerly used in the United Kingdom.

C₁₄H₂₂N₂O,HCl,H₂O   M.m. = 288.8 g/mol

DEFINITION

Lidocaine hydrochloride contains not less than 99.0 per cent and not more than the equivalent of 101.0 per cent of 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide hydrochloride, calculated with reference to the anhydrous substance.

CHARACTERS

A white, crystalline powder, very soluble in water, freely soluble in alcohol.

Obtaining

Initial substance for lidocaine obtaining is 2,6-dimethylanilide, which acetylizes by means of acid chloride chloracetic acid Cl–CH₂–CO–Cl, and then condense with diethylamine in benzene at presence of chloride acid HCl:

IDENTIFICATION

First identification A, B, F.

Second identification A, C, D, E, F.

 A. Melting point (2.2.14): 74 °C to 79 °C, determined without previous drying.

 B. Examine by infrared absorption spectrophotometry (2.2.24), comparing with the spectrum obtained with lidocaine hydrochloride CRS.

 C. Interaction with picric acid. Dissolve 0.2 g in 10 ml of water R and add 10 ml of picric acid solution R. The precipitate, washed with water R and dried, melts (2.2.14) at about 230 °C.

 D. To about 5 mg add 0.5 ml of fuming nitric acid R. Evaporate to dryness on a water-bath, cool and dissolve the residue in 5 ml of acetone R. Add 0.2 ml of alcoholic potassium hydroxide solution R. A green colour is produced.

 E. Reaction with cobalt (ІІ) nitrate. To 5 ml of solution S (see Tests) add 5 ml of water R and make alkaline with dilute sodium hydroxide solution R. Collect the precipitate on a filter and wash with water R. Dissolve half of the precipitate in 1 ml of alcohol R and add 0.5 ml of a 100 g/l solution of cobalt nitrate R. A bluish-green precipitate is formed.

 F. It gives reaction (a) of chlorides (2.3.1).

AgNO₃ + Lidocaine×HCl ® AgCl↓ + Lidocaine ×HNO₃

white

AgCl + 2NH₄OH ® [Ag(NH₃)₂]Cl + 2H₂O

Other reaction of identification:

1. Alkaline hydrolysis of drug with the next identification of 2,6-dimethylaniline:

a) Formation azo dye of orange or red colour (this is reaction diazotization with the next azocoupling (presence of a primary aromatic amino group)):

azo dye of orange or red colour

b) Formation azomethine dye (Schiff base) (at interaction with acetone СН₃СОСН₃ (presence of a primary aromatic amino group):

2. Alkaline hydrolysis of drug with the next identification sodium 2-diethylaminoacetate. The second product of alkaline hydrolysis – sodium 2- diethylaminoacetate concerns to tertiary amine, having characteristic smell.

characteristic smell

TESTS

Solution S

Dissolve 1.0 g in carbon dioxide-free water R and dilute to 20 ml with the same solvent.

Appearance of solution

Solution S is clear (2.2.1) and colourless (2.2.2, Method II).

pH (2.2.3)

Dilute 1 ml of solution S to 10 ml with carbon dioxide-free water R. The pH of the solution is 4.0 to 5.5.

Impurity A

Solution (a) Dissolve 0.25 g of the substance to be examined in methanol R and dilute to 10 ml with the same solvent. This solution is used to prepare the test solution.

Solution (b) Dissolve 50 mg of 2,6-dimethylaniline R in methanol R and dilute to 100 ml with the same solvent. Dilute 1 ml of the solution to 100 ml with methanol R. This solution is used to prepare the standard.

Using three flat-bottomed tubes, place in the first 2 ml of solution (a), in the second 1 ml of solution (b) and 1 ml of methanol R and in the third 2 ml of methanol R (used to prepare a blank). To each tube add 1 ml of a freshly prepared 10 g/l solution of dimethylaminobenzaldehyde R in methanol R and 2 ml of glacial acetic acid R and allow to stand at room temperature for 10 min. The intensity of the yellow colour of the test solution is between that of the blank and that of the standard (100 ppm).

Heavy metals (2.4.8)

Dissolve 1.0 g in water R and dilute to 25 ml with the same solvent. Carry out the prefiltration. 10 ml of the prefiltrate complies with limit test E for heavy metals (5 ppm). Prepare the standard using 2 ml of lead standard solution (1 ppm Pb) R.

Water (2.5.12)

5.5 per cent to 7.0 per cent, determined on 0.25 g by the semi-micro determination of water.

Sulphated ash (2.4.14)

Not more than 0.1 per cent, determined on 1.0 g.

IMPURITIES

 A. 2,6-dimethylaniline.

ASSAY (Ph Eur) of Lidocaine (Ointment) (2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide)

Acidimetry, non-agueous titration

To 0.200 g add 50 ml of anhydrous acetic acid R and stir until dissolution is complete. Titrate with 0.1 M perchloric acid, determining the end-point potentiometrically (2.2.20).

1 ml of 0.1 M perchloric acid is equivalent to 23.43 mg of C₁₄H₂₂N₂O.

SPU : direct titration of solution test substance in anhydrous acetic acid R СН₃СООН with standard solution perchloric acid HClO₄ at presence merccury (ІІ) acetate Hg (CH₃COO) ₂ (for bound of chlorides-ions in the form of slightly soluble salt) and uses crystal violet as indicator.

Е_m (С₁₄Н₂₂N₂O×HCl) = М m.

ASSAY (Ph Eur) of Lidocaine hydrochloride (2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide hydrochloride)

Dissolve 0.220 g in 50 ml of alcohol R and add 5.0 ml of 0.01 M hydrochloric acid. Carry out a potentiometric titration (2.2.20), using 0.1 M sodium hydroxide. Read the volume added between the 2 inflexion points.

1 ml of 0.1 M sodium hydroxide is equivalent to 27.08 mg of C₁₄H₂₃ClN₂O.

Ph Eur

Other methods of assay:

Argentometry (for fixed(boud, combined) HCl)

a) Faience Method. Direct titration of an investigated solution with standard solution of AgNO₃ in acetic-acid medium СН₃СООН, using bromthymol dark blue as indicator.

AgNO₃ + Lidocaine×HCl ® AgCl↓ + Lidocaine ×HNO₃

Е_m (С₁₄Н₂₂N₂O×HCl) = М m.

b) Volhard method, back titration. To investigated solution add double excess of standard solution of AgNO₃. Excess of AgNO₃ titrate with standard solution of NH₄SCN in the presence of ammonium iron alum (NH₄) Fe (SO₄) ₂ as indicator before red-pink colouring.

Lidocaine ×HCl + AgNO₃ ® Lidocaine ×HNO₃ + AgCl↓

AgNO₃ + NH₄SCN ® AgSCN¯ + NH₄NO₃

3NH₄SCN + (NH₄)Fe(SO₄)₂ ® Fe(SCN)₃ + 2(NH₄)₂SO₄

red-pink colouring

Е_m (С₁₄Н₂₂N₂O×HCl) = М m.

STORAGE

Store protected from light.

Action and use

Local anaesthetic; anti-arrhythmic.

Preparations

Lidocaine Gel

Lidocaine and Chlorhexidine Gel

Lidocaine Injection

Lidocaine and Adrenaline Injection/Lidocaine and Epinephrine Injection

Sterile Lidocaine Solution

Ph Eur

Trimecaine hydrochloride

Trimecainum

С₁₅Н₂₄N₂O×HCl

М m. = 283,93 g/mol

The chemical name:a-diethylamino-2,4,6-trimethylacetanilide hydrochloride

Differs from lidocaine only presence of one more methyl group –СН₃ (in position 4 phenylic ring).

Obtaining (it is similar to lidocaine).

Interaction acid chloride chloroacetic acid Cl–CH₂–C (O)–Cl with 2,4,6-trimethylaniline (mesidine), and then condensation with diethylamine (С₂Н₅) ₂NH at presence of chloride acid HCl:

Properties

The description. White or slightly yellowish crystal powder. Melting point of 136–137 °C.

Solubility. Very soluble in water, freely soluble in alcohol and chloroform, it is practically insoluble in ether. рН water solution 4,5–5,2. Solutions prepare on an isotonic solution of sodium chloride, sterilise at +100 °C within 30 minutes.

Identification

1. Acid or alkaline hydrolysis of drug with the next identification 2,4,6-trimethylaniline (presence of primary aromatic amino group):

a) Formation azo dye (orange or red colour) at reaction diazotization (with solution of sodium nitrite NaNO₂ and chloride acid HCl) with the next azocoupling (with alkaline solutionb-naphthol):

mesidine

azo dye of red colour

b) Formation azomethine dye (Schiff base) at interaction with acetone СН₃СОСН₃:

2. Alkaline hydrolysis of test substance with the next identification of sodium 2-diethylaminoacetate. The second product of alkaline hydrolysis – sodium 2-diethylaminoacetate concerns to tertiary amines, having a characteristic smell.

characteristic smell

3. Reaction (a) on chlorides.

AgNO₃ + Trimecaine×HCl ® AgCl↓ + Trimecaine ×HNO₃

white

AgCl + 2NH₄OH ® [Ag(NH₃)₂]Cl + 2H₂O

4. Reaction with formaldehyde and alkali with formation of isonitrile.

5. Oxidation alkyl radicals to carboxylic group –СООН.

6. Nitrogene definition by means of Keldal method (for qualitative and quantitative definition).

For difference Trimecaine from lidocaine use such reactions:

1. Oxidation of Trimecaine by mix of copper(ІІ) sulphate CuSO₄ and concentrated sulphatic acid H₂SO₄ at heating. After mix cooling, add the concentrated solution of ammonia NH₄OH; there is a dark blue colouring, and in UV-light red-pink fluorescence is observed.

2. Microcrystalloscopic reaction. Oxidation of Trimecaine by chromic mix. At interaction of Trimecaine with solution of K₂Cr₂O₇ and sulphatic acid H₂SO₄ crystals in the form of the needles collected in bunches are formed.

Assay (it is similar to lidocaine)

1. Nitritometry, after acid hydrolysis, direct titration with standard solution of sodium nitrite NaNO₂ in chloride-acid medium HCl and presence of KBr as catalyst with use external (potassium iodide test paper) or internal (tropeolin 00, mix tropeolin 00 with methylene dark blue, etc.) indicators.

Е_m (С₁₅Н₂₄N₂O×HCl) = М m.

2. Acidimetry, non-aqueous titration: direct titration of solution Trimecaine in anhydrous СН₃СООН with standard solution of HClO₄ at presence mercury(ІІ) acetate Hg (CH₃COO) ₂ (for bond of chlorides-ions in the form of slightly soluble salt) and the indicator – crystal violet.

Е_m (С₁₅Н₂₄N₂O×HCl) = М m.

In parallel spend control experience.

3. Argentometry (for fixed(boud, combined) HCl)

a) Faience Method. Direct titration of an investigated solution with standard solution of AgNO₃ in acetic-acid medium СН₃СООН, using bromthymol dark blue as indicator.

AgNO₃ + Trimecaine ×HCl ® AgCl↓ + Trimecaine ×HNO₃

white

Е_m (С₁₅Н₂₄N₂O×HCl) = М m.

b) Volhard method, back titration. To investigated solution add double excess of standard solution of AgNO₃. Excess of AgNO₃ titrate with standard solution of NH₄SCN in the presence of ammonium iron alum (NH₄) Fe (SO₄) ₂ as indicator before red-pink colouring.

Trimecaine ×HCl + AgNO₃ ® Trimecaine ×HNO₃ + AgCl↓

AgNO₃ + NH₄SCN ® AgSCN¯ + NH₄NO₃

3NH₄SCN + (NH₄)Fe(SO₄)₂ ® Fe(SCN)₃ + 2(NH₄)₂SO₄

red-pink colouring

Е_m (С₁₅Н₂₄N₂O×HCl) = М m.

4.Mercurymetry: direct titration with standard solution of mercury(ІІ) nitrate Hg (NO₃) ₂ at presence of HNO₃ and the indicator diphenylcarbazone:

2R×HCl + Hg(NO₃)₂ ® HgCl₂ + 2R×HNO₃

The excess drop of titrant Hg (NO₃) ₂ reacts with diphenylcarbazone with formation chelate of Mercury of pink-violet colouring:

Е_m (С₁₅Н₂₄N₂O×HCl) = М m.

5. Alkalimetry water solution of Trimecaine in the presence of chloroform (for bounded HCl): direct titration with solution of NaOH in the presence of organic solvent (chloroform or a mix of chloroform with alcohol, for infusion the insoluble trimekaine-base in water) and the indicator phenolphthalein to light-pink colourings.

Trimecaine ×HCl + NaOH ® Trimecaine ¯ + NaCl + H₂O

Е_m (С₁₅Н₂₄N₂O×HCl) = М m.

Storage. In densely corked container, in the place protected from light. The list of strong substances.

Application. Active local anesthetic.

On a chemical structure and pharmacological action similarly to lidocaine. To similarly lidocaine, is not the competitor sulphanylamide drugs. In force and duration of action surpasses procaine hydrochloride. Causes fast, deep and long anaesthesia, and at higher concentration (2–5 %) – and superficial anaesthesia. It is a little toxic, does not show irritating action.

Shows also antiarrhytmic action, but less expressed in comparison with lidocaine.

Release forms: powder, 0,25 % solution in ampoules on 10 ml; 0,5 % and 1 % solutions in ampoules on 2,5 and 10 ml; 2 % solution – on 1; 2; 5 and 10 ml; 5 % asolution – on 1 and 2 ml, is a part of an aerosol.