Alcohols.
All alcohols, а principle, can be divided into two broad categories i.е. aliphatic alcohols und aromatic alcohols.
1. Aliphatic alcohols. Alcohols in which the hydraryl group is linked an aliphatic carbon chain are called aliphatic alcohols.
For example,
Methyl alcohol Ethyl alcohol Isopropyl alcohol
Methanol Ethanol 2-Propanol
2. Aromatic alcohols. Alcohols in which the hydroxyl group is present in the side chain of an aromatic hydrocarbon are called aromatic For example.
phenylmethanol 2-phenylethanol
(benzyl alcohol) (b–phenylethyl alcohol)
Alcohols are further classified as monohydric, dihydric, trihydric and рolyhydric according as their molecules contain one, two, three, or many hydroxyl groups respectively. For ехашр1е,
Ethyl alcohol 1,2-Ethanediol 1,2,3-propanetriol
(Monohydric) (Dihydric) (Trihydric)
Nomenclature of alcohols. As with most other classes of organic compounds, alcohols can be named in several ways. Commoames are useful only for the simpler members of а class. However, commoames are widely used in colloquial conversation and in the scientific literature. In order to communicate freely, the student must know commoames. Since the systematic IUPAC names are often used for indexing the scientific literature, the student must be thoroughly familiar with systematic names in order to retrieve data from the literature.
1.Тhe alkyl alcohol system. In this system of commoomenclature, the name of an alcohol is derived by combining the name of the alkyl group with the word alcohol. The names are mitten as two words.
n-butyl alcohol isobutyl alcohol t-butyl alcohol
2. In this common system, the position of an additional substituent is indicated by use of the Greek alphabet rather than by numbers.
b–chloroethyl alcohol g–bromobutyl alcohol
This use of the Greek alphabet is widespread in organic chemistry and it is important to learn the first few letters, at least through delta. Many of the letters, small and capital, have evolved standard meanings in the mathematical and physical sciences (for example, the number p). In organic chemistry, the lower case letters are used more frequently than the capital letters.
The last letter of the Greek alphabet is omega, w. Correspondingly, this letter is used to refer to difunctional compounds when the secondary substituent is on the end carbon of the chain.
Br(CH2)nOH w–bromo alcohols
Any simple radical that has а commoame may be used in the alkyl alcohol system, with one important exception. The grouping С6Н5 – has the special name phenyl, but the compound C6H5OH is phenol, not phenyl alcohol.
phenol
Substituted phenols are named as derivatives of the parent compound phenol. The reason for this difference is historical and arose from the fact that phenol and its derivatives have many chemical properties that are very different from those of alkyl alcohols. However, phenyl substituted alkyl alcohols are normal alcohols and often have commoames.
Examples are:
phenylmethanol 2-phenylethanol
(benzyl alcohol) (b–phenylethyl alcohol)
3. The carbinol system. In this system, the simplest alcohol, СН3ОН, is called carbinol. More complex alcohols are named as alkyl substituted carbinols. The names are written as one word.
ethylmethylcarbinol triethylcarbinol methylphenilcarbinol
The number of carbons attached to the carbinol carbon distinguishes primary, secondary, and tertiary carbinols. As in the case of the alkyl halides, this classification is useful because the different types of alcohols show important differences in reactivity under given conditions. The carbinol system of nomenclature has been falling into disuse in recent years. However, it is found extensively in the older organic chemical literature.
IUPAC rules for naming alcohols that contain а single hydroxyl group follow.
Rule 1: Name the longest carbon’ chain to which the hydroxyl group is attached. The chaiame is obtained by dropping the final -е from the alkane name and adding the suffix –ol. – alkanols.
СН3ОН СН3СН2ОН
methanol ethanol
Rule 2: Number the chain starting at the end nearest the hydroxyl group, and use the appropriate number to indicate the position of the – ОН group. (In numberin of the longest carbon chain, the hydroxyl group has priority over double an triple bonds, as well as over alkyl, cycloalkyl, and halogen substituents.)
Rule 3: Name and locate any other substituents present.
Rule 4: In alcohols where the – ОН group is attached to а carbon atom in а ring, the hydroxyl group is assumed to be on carbon 1.
In the naming of alcohols with unsaturated carbon chains, two endings are needed: one for the double or triple bond and one for the hydroxyl group. The –ol suffix always comes last in the name; that is, unsaturated alcohols are named as alkenols or alkynols.
Polyhydroxy alcohols — alcohols that possess more than one hydroxyl group – can be names with only а slight modification of the preceding IUPAC rules. An alcohol in which two hydroxyl groups are present is named as а diol, one containing three hydroxyl groups is named as а triol, and so on. In these names for diols, triols, and so forth, the final –е of the parent alkane name is retained for pronunciation reasons.
1,2-Ethanediol 1,2-propanediol 1,2,3-propanetriol
Monohydroxy alcohols are hydrocarbon derivatives which contain only one group –OH connected with sp3-hybridizated carbon atom.
The general formula of monohydroxy alcohols is:
The names of monohydroxy alcohols are the names of the same hydrocarbons with added prefix –ol.
Classification of monohydric alcohols. As already mentioned, alcohols containing one ОН group per molecule are called monohydric alcohols. These are further classified as primary (1′), secondary (2′), and tertiary (3′) according as the ОН group is attached to primary, secondary and tertiary carbon atoms respectively. For example:
Ethanol Isopropyl alcohol 2-Methylpropanan 2-ol
Primary alcohol Secondary alcohol Tertiary alcohol
Monohydroxy alcohols are characterized by structural, geometrical and optical isomery. Structural isomery depends on different structure of carbon chain and different locations of –OH group.
For unsaturated monohydroxy alcohols structural isomery depends on different locations of double bond too.
Only unsaturated monohydroxy alcohols are characterized by geometrical isomery.
Optical isomery is characteristic for alcohols which have asymmetric carbon atom in their structure.
The methods of extraction
Alcohols can be obtained from many other classes of compounds. Preparations from alkyl halides and from hydrocarbons will be discussed in this section. The following important ways of prераring alcohols will be discussed later, as reactions of the appropriate functional groups.
1. Hydrolysis of halogenderivatives of hydrocarbons by heating:
CH3−CH2−Cl + NaOH → CH3−CH2−OH + NaCl
2. Hydrogenation of alkenes. This reaction runs by Markovnikov rule.
3. Reduction of carbonyl compounds (aldehydes, ketones, carboxylic acids, complex ethers):
\
1. Reduction of carboxylic acids:
Physical properties
Saturated alcohols are colourless liquids and crystal solids with peculiar smell. The smallest representatives of homological row have smell of alcohol, but higher representatives have good smell. The lower alcohols e liquids with characteristic odors and sharp tastes. One striking feature is their relatively high boiling points. The ОН group is roughly equivalent to а methyl group in approximate size and polarizability, but alcohols have much higher boiling points than the corresponding hydrocarbons; for example, compare ethanol (mol. wt. 46, b.р.78.50) and propane (mol. wt. 44, b.р. – 420).
The abnormally high boiling points of alcohols are the result of а special type of dipolar association in the liquid phase. Both the С – О and the О – Н bonds are polar because of the different electronegativities of carbon, oxygen, and hydrogen. These polar bonds contribute to the substantial dipole moments.
However, the dipole moments of alcohols are no greater than those of corresponding chlorides.
СН3ОН, m = 1.71 D СН3Сl m= 194 D
СН3СН3ОН, m = 1.70 D СН3СН2Сl, m = 2.04 D
For alcohols the negative end of the dipole is out at the oxygen lone pairs, and the positive end is close to the small hydrogen. For hydrogen atoms bonded to electronegative elements dipole-dipole interaction is uniquely important and is called а hydrogen bond. This proximity of approach is shown by bond distance data. The O – Н bond length in alcohols is 0.96 А. The hydrogen bonded Н. . .O distance is 2.07 А, about twice as large. In fact, this distance is sufficiently small that some hydrogen bonds may have а significant amount of covalent or shared electron character.
Methanol and ethanol are reasonably good solvents for salt-like compounds. Because they are also good solvents for organic compounds, they are used frequently for organic reactions such as SN2 displacement reactions.
The ОН group of alcohols can participate in the hydrogen bond network of water. The lower alcohols are completely soluble in water. As the hydrocarbon chain gets larger, the compound begins to look more like an alkane, and more of the hydrogen bonds in water must be broken to make room for the hydrocarbon chain. Since the hydrogen bonds that are lost are not completely compensated by bonding to the alcohol ОН, solubility decreases as the hydrocarbon chain gets larger. А rough point of division is four carbons to one oxygen. Above this ratio, alcohols tend to have little solubility in water. This guideline is only approximate because the shape of the hydrocarbon portion is also important. t-Butyl alcohol is much more soluble than и-butyl alcohol because the t-butyl group is more compact and requires less room or broken water hydrogen bonds in an aqueous solution. А similar phenomenon is seen with the branched pentyl alcohols.
Chemical properties
Alcohols are classified as primary (1′), secondary (2′), or tertiary (3′), depending on the number of carbon atoms bonded to the carbon atom that bears the hydroxyl group. А primary alcohol is an alcohol in which the hydroxyl-bearing carbon atom is attached to only one other carbon atom. А secondary alcohol is an alcohol in which the hydroxyl-bearing carbon atom is attached to two other carbon atoms. А tertiary alcohol is an alcohol in which the hydroxyl-bearing carbon atom is attached to three other carbon atoms. Chemical reactions of alcohols often depend on alcohol class (1′, 2′, or 3′).
In general, alcohols (1′, 2′, and 3′) are very flammable substances that, when burned, produce carbon dioxide and water. Additional important reactions of alcohols besides combustion include
1. Intramolecular dehydration to produce an alkene
2. Intermolecular dehydration to produce an ether
3. Oxidation to produce aldehydes, ketones, and carboxylic acids
4. Substitution reactions to produce alkyl halides
1. Alcohols have weak acidic and weak alkaline properties. They can react with alkaline metals like acids and form alkoxides:
2CH3CH2OH + 2Na → 2CH3CH2ONa + H2↑
2CH3CH2ONa + H2O ↔ CH3CH2OH + NaOH
2. Alcohols can react with mineral and organic acids (complex ethers form) like alkalis:
CH3CH2OH + HONO2 ↔ CH3CH2ONO2 + HOH
3. Dehydration of alcohols. There are 2 types of dehydration:
a) Dehydration between 2 molecules:
b) Dehydration in the molecule:
4. Reaction with HI, HCl, HBr:
CH3CH2OH + HI → CH3CH2I + H2O
5. Oxidation
Primary and secondary alcohols readily undergo oxidation in the presence of mild oxidizing agents to produce compounds that contain а carbon — oxygen double bond (aldehydes, ketones, and carboxylic acids). А number of different oxidizing agents can be used for the oxidation, including potassium permanganate (КМnO4), potassium dichromate (К2Сr2О7), and chromic acid (H2CrO4).
The net effect of the action of а mild oxidizing agent on а primary or secondary alcohol is the removal of two hydrogen atoms from the alcohol. One hydrogen comes from the – ОН group, the other from the carbon atom to which the -ОН group is attached. This Н removal generates а carbon — oxygen double bond. The two “removed” hydrogen atoms combine with oxygen supplied by the oxidizing agent to give H2O.
Primary alcohol = aldehyde = carboxylic acid
Secondary alcohol = ketone
Tertiary alcohol = no reaction
The general reaction for the oxidation of а primary alcohol is
Alcohol Aldehyde Carboxylic acid
In this equation, the symbol [O] represents the mild oxidizing agent. The immediate product of the oxidation of а primary alcohol is an aldehyde. Because aldehydes themselves are readily oxidized by the same oxidizing agents that oxidize alcohols, aldehydes are further converted to carboxylic acids. А specific example of а primary alcohol oxidation reaction is
The three classes of alcohols behave differently toward mild oxidizing agents.
The general reaction for the oxidation of а secondary alcohol is
Alcohol Ketone
As with primary alcohols, oxidation involves the removal of two hydrogen atoms. Unlike aldehydes, ketones are resistant to further oxidation. А specific example of the oxidation of а secondary alcohol is
Tertiary alcohols do not undergo oxidation with mild oxidizing agents. This is because they do not have hydrogen on the -ОН-bearing carbon atom.
Alcohol
To determine any alcohol (which contain fragment in the mixture of compounds it is needed to use iodoform test. As the result yellow precipitate forms.
Secondary alcohols are oxidized to ketones by the same reagents that oxidize primary
alcohols:
1. Di-, tri- and polihydroxy alcohols
Dihydroxy alcohols contain two groups –OH in the molecule. They are called diols. There are several types of diols.
1. α-diols (groups –OH are situated near neighboring carbon atoms in 1,2-locations);
2. β-diols (groups –OH are situated in 1,3-locations);
3. γ-diols (groups –OH are situated in 1,4-locations) etc.
Trihydroxy alcohols contain three groups –OH in the molecule. They are called triols. The representative is glycerol:
PREPARATION OF DIOLS
1. Much of the chemistry of diols—compounds that bear two hydroxyl groups—is analogous to that of alcohols. Diols may be prepared, for example, from compounds that contain two carbonyl groups, using the same reducing agents employed in the preparation of alcohols. The following example shows the conversion of a dialdehyde to a diol by catalytic hydrogenation. Alternatively, the same transformation can be achieved by reduction with sodium borohydride or lithium aluminum hydride.
2. Since osmium tetraoxide is regenerated in this step, alkenes can be converted to vicinal diols using only catalytic amounts of osmium tetraoxide, which is both toxic and expensive. The entire process is performed in a single operation by simply allowing a solution of the alkene and tert–butyl hydroperoxide in tert–butyl alcohol containing a small amount of osmium tetraoxide and base to stand for several hours.
Overall, the reaction leads to addition of two hydroxyl groups to the double bond
and is referred to as hydroxylation. Both oxygens of the diol come from osmium tetraoxide via the cyclic osmate ester. The reaction of OsO4 with the alkene is a syn addition, and the conversion of the cyclic osmate to the diol involves cleavage of the bonds between oxygen and osmium. Thus, both hydroxyl groups of the diol become attached to the same face of the double bond; syn hydroxylation of the alkene is observed.
To extract glycerol it is necessary to use next reaction:
Chemical properties
1. Reaction with alkaline metals
2. Reaction with Cu(OH)2
3. Reaction with HI, HCl, HBr:
4. Formation of simple and complex ethers (reaction with monohydroxy alcohols and organic acids):
5. Reaction with mineral acids:
6. Oxidation by KMnO4
7. Dehydration
8. Policondensation
9. Diols react intramolecularly to form cyclic ethers when a five-membered or sixmembered ring can result.
2. Thioalcohols
Thioalcohols are compounds which contain aliphatic (CnH2n+1) and mercaptane (−SH) groups. Thiols are given substitutive IUPAC names by appending the suffix –thiol to the name of the corresponding alkane, numbering the chain in the direction that gives the lower locant to the carbon that bears the −SH group.
The preparation of thiols involves nucleophilic substitution of the SN2 type on alkyl
halides and uses the reagent thiourea as the source of sulfur. Reaction of the alkyl halide with thiourea gives a compound known as an isothiouronium salt in the first step. Hydrolysis of the isothiouronium salt in base gives the desired thiol (along with urea):
Both steps can be carried out sequentially without isolating the isothiouronium salt.
To extract thioalcohols it is necessary to use next reactions:
1. C2H5Cl + NaSH → C2H5SH + NaCl
2. C2H5OH + Na2S → C2H5SH + H2O
PROPERTIES OF THIOLS
When one encounters a thiol for the first time, especially a low-molecular-weight thiol, its most obvious property is its foul odor. Ethanethiol is added to natural gas so that leaks can be detected without special equipment—your nose is so sensitive that it can detect less than one part of ethanethiol in 10,000,000,000 parts of air! The odor of thiols weakens with the number of carbons, because both the volatility and the sulfur content decrease. 1-Dodecanethiol, for example, has only a faint odor.
The S–H bond is less polar than the O–H bond, and hydrogen bonding in thiols
is much weaker than that of alcohols. Thus, methanethiol (CH3SH) is a gas at room
temperature (bp 6°C), and methanol (CH3OH) is a liquid (bp 65°C).
Chemical properties:
1. Thiols can react with ions of alkaline and heavy metals (this property of thiols is used in medicine by poisoning of heavy metals):
C2H5SH + NaOH → C2H5S−Na+ + H2O
2C2H5SH + Hg2+ → (C2H5S)2Hg + 2H+
2. They can react with alkenes (peroxides are catalysts):
3. Reaction with organic acids:
4. Oxidation
Amino alcohols are organic compounds that contain both an amine functional group and an alcohol functional group
NH2-CH2-CH2-OH N(C2H5)-CH2-CH2-OH
2-aminoethanol 2-N,N– diethylaminoethano
If the molecule of amino alcohol contains the in its composition two or three hydroxyalkylnes groups, through the combination of nitrogen atom, in this case, the basis takes the name amine.
OH-CH2-CH2-NH-CH2-CH2-OH
di (β–oxyethyl) amine, or di (2-hydroxyethyl) amine
Ethanolamine, also called 2-aminoethanol or monoethanolamine (often abbreviated as ETA or MEA), is an organic chemical compound that is both a primary amine (due to an amino group in its molecule) and a primary alcohol (due to a hydroxyl group). Like other amines, monoethanolamine acts as a weak base.
Monoethanolamine is produced by reacting ethylene oxide with aqueous ammonia; the reaction also produces diethanolamine and triethanolamine. The ratio of the products can be controlled by changing the stoichiometry of the reactants.
Note that this reaction is exothermic and that controls are needed to prevent a runaway reaction.
Enols (also known as alkenols) are alkenes with a hydroxyl group affixed to one of the carbon atoms composing the double bond. Enols and carbonyl compounds (such as ketones and aldehydes) are in fact isomers; this is called keto-enol tautomerism:
The enol form is shown above on the left. It is usually unstable, does not survive long, and changes into the keto (ketone) form shown on the right. This is because oxygen is more electronegative than carbon and thus forms stronger multiple bonds. Hence, a carbon-oxygen (carbonyl) double bond is more than twice as strong as a carbon-oxygen single bond, but a carbon-carbon double bond is weaker than two carbon-carbon single bonds.
Only in 1,3-dicarbonyl and 1,3,5-tricarbonyl compounds does the (mono)enol form predominate. This is because the resonance and intermolecular hydrogen bonding that occurs in the enol form is not possible in the keto form. Thus, at equilibrium, over 99% of propanedial (OHCCH2CHO) molecules exist as the monoenol. The percentage is lower for 1,3-aldehyde ketones and diketones. Enols (and enolates) are important intermediates in many organic reactions.
The name of enols systematic nomenclature IUPAC form the name alkene to which is added the suffix-ol:
CH2=CH-OH CH2=CH-CH2-OH
ethenol, vinyl alcohol Propenol-1(unsaturated alcohol)
Hydration of acetylene as the intermediate substance is formed vinyl alcohol (enol), which isomerization in acetic aldehyde.
This property of enols characterizes the rule of Eltekov-Erlenmeyer. – Compounds in which the hydroxyl group located at carbon atoms that forms a fold communication, unstable and isomerization of carbonyl compounds – aldehydes and ketones
The methods of extraction of amino alcohols
1. Accession of ammonia or amines to the α–oxyses.
CH2-CH2 + NH3 = NH2-CH2-CH2-OH
O
2. Reduction of nithroarenes.
CH3–CH(NO2)-CH2-OH + 3H2 = CH3-CH(NH3)-CH2-OH + 2H2O
Chemical properties of amino alcohols
1. Amino alcohols show properties as alcohols and amines. As a basis amino alcohols form salts with mineral acids.
OH-CH2-CH2–NH2 + HCl = OH-CH2-CH2-NH3 +Cl¯
The words enol and alkenol are portmanteaux of the words alkene (or just –ene, the suffix given to alkenes) and alcohol (which represents the enol’s hydroxyl group).
Methyl alcohol (Methanol). Methyl alcohol, with one carbon atom and one — ОН group, is the simplest alcohol. This colorless liquid is а good fuel for internal combustion engines. Since 1965 all racing cars at the Indianapolis Speedway have been fueled with methyl alcohol. (Methyl alcohol fires are easier to put out than gasoline fires, because water mixes with and dilutes methyl alcohol.) Methyl alcohol also has excellent solvent properties, and it is the solvent of choice for paints, shellacs, and varnishes.
Methyl alcohol is sometimes called wood alcohol, terminology that draws attention to an early method for its preparation — the heating of wood to а high temperature in the absence of air. Today, almost all methyl alcohol is produced via the reaction between H2 and СО.
Drinking methyl alcohol is чету dangerous. Within the human body, methyl alcohol is oxidized by the liver enzyme alcohol dehydrogenase to the toxic metabolites formaldehyde and formic acid.
Formaldehyde is toxic to the eye and can cause blindness (temporary or permanent). Formic acid causes acidosis. Ingesting as little as 1 oz (30 ml.) of methyl alcohol can cause optic nerve damage.
Ethyl alcohol (Ethanol), the two-carbon monohydroxy alcohol, is the alcohol present in alcoholic beverages and is commonly referred to as simply alcohol or drinking alcohol. Like methyl alcohol, ethyl alcohol is oxidized in the human body by the liver enzyme alcohol dehydrogenase.
Acetaldehyde, the first oxidation product, is largely responsible for the symptoms of hangover. The odors of both acetaldehyde and acetic acid are detected on the breath of someone who has consumed а large amount of alcohol. Ethyl alcohol oxidation products are less toxic than these of methyl alcohol.
Long-term excessive use of ethyl alcohol may cause undesirable effects such as cirrhosis of the liver, loss of memory, and strong physiological addiction. Links have also been established between certain birth defects and the ingestion of ethyl alcohol by women during pregnancy (fetal alcohol syndrome).
Ethyl alcohol can be produced by yeast fermentation of sugars found in plant extracts. The synthesis of ethyl alcohol in this manner, from grains such as corn, rice, and barley, is the reason why ethyl alcohol is often called grain alcohol.
Denatured alcohol is ethyl alcohol that has been rendered unfit to drink by the addition of small amounts of toxic substances (denaturing agents). Almost all of the ethyl alcohol used for industrial purposes is denatured alcohol.
Most ethyl alcohol used in industry is prepared from ethene via а hydration reaction
The reaction produces а product that is 95% alcohol and 5% water. In applications where water does interfere with use, the mixture is treated with а dehydrating agent to produce 100% ethyl alcohol. Such alcohol, with all traces of water removed, is called absolute alcohol.
Isopropyl alcohol (2-propanol) is one of two three-carbon monohydroxy alcohols; the other is propyl alcohol. А 70% isopropyl alcohol — 30% water solution marketed as rubbing alcohol. Isopropyl alcohol’s rapid evaporation rate creates а dramatic cooling effect when it is applied to the skin, hence its use for alcohol rubs to combat high body temperature.
Isopropyl alcohol has а bitter taste. Its toxicity is twice that of ethyl alcohol but causes few fatalities because it often induces vomiting and thus doesn‘ t stay down long enough to kill you. In the body it is oxidized to acetone.
Large amounts, about 150 mL, of ingested isopropyl alcohol can be fatal; death occurs from paralysis of the central nervous system.
Ethylene glycol (1,2-ethanediol) and propylene glycol (1,2-propanediol) are the two simplest alcohols possessing two – ОН groups. Besides being diols, they are also classified as glycols. А glycol is а diol in which the two – ОН groups are on adjacent carbon atoms.
Both of these glycols are colorless, odorless, high-boiling liquids that are completely miscible with water. Their major uses are as the main ingredient in automobile “year-round” antifreeze and airplane “de-icers” and as а starting material for the manufacture of polyester fibers.
Ethylene glycol is extremely toxic when ingested. In the body, liver enzymes oxidize it to oxalic acid. Oxalic acid, as а calcium salt, crystallizes in the kidneys, which leads to renal problems.
On the other hand, propylene glycol is essentially nontoxic and has been used as а solvent for drugs. Like ethylene glycol, it is oxidized by liver enzymes; however, pyruvic acid, its oxidation product, is а compound normally found in the human body, being an intermediate in carbohydrate metabolism.
Glycerol (1,2,3-propanetriol) is а clear, thick liquid that has the consistency of honey. Its molecular structure involves three ОН groups on three different carbon atoms.
