Alcohol

Alcohols are compounds which has got OH group as their functional group. Alcohols are present naturally in many product like ethanol and methanol.

Alcohols are classified with number of OH groups attached. For example when the alcohol contains only one OH it is called as mono hydric alcohol for example ethanol whose formula is CH₃CH₂OH, when the compound contains two OH group it is called as di hydric alcohol for example as in ethylene glycol CH₂OH-CH₂OH. The alcohol is called as tri hydric alcohol when there is three OH group attached in the compound for example as in glycerol CH₂OH-CHOH-CH₂OH.
Another important way of classifying the alcohol is by the carbon in which the alcohol is attached.

What is Alcohol?

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Alcohol is an organic compound containing hydroxyl functional group. Ethanol a main constituent of beverages and medicines and glycol common antifreeze are some examples of alcohols.

The general formula of alcohol is R-OH, where R can be alkyl group. Depending on the nature of alkyl group (R) the alcohol are classified as primary, secondary, tertiary, vinyl, allyl and benzyl alcohol.

Synthesis of Alcohols

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Alcohols can be synthesized by any of the following ways.

1. By the hydration of alkenes

Alkenes on hydration in the presence of dilute acids give alcohols. For example ethylene on hydration gives ethyl alcohol.

CH₂=CH₂ + H₂O → CH₃-CH₂-OH

Hydration of propene gives 2-propanol in according to Markovnikov's rule. The reaction involves protonation of alkene followed by addition of water.

2. By reduction of aldehydes, ketones, acyl chlorides

Alcohols are synthesized by reduction of aldehyde with lithium aluminum hydride. Reduction of aldehyde generally gives primary alcohols. For example acetaldehyde on reduction gives ethyl alcohol.

CH₃-CHO → CH₃-CH₂-OH

Similarly ketones on reduction give secondary alcohols. For example ketone on reduction gives 2-propanol.

Acyl chlorides like acetyl chloride on strong reduction give alcohols. Acetyl chloride on strong reduction gives ethyl alcohol.

CH₃-COCl → CH₃CHO → CH₃-CH₂-OH

3. By hydrolysis of Grignard reagent

Grignard reagent like methyl magnesium chloride reacts with formaldehyde to give a primary alcohol. Here methyl magnesium chloride reacts with formaldehyde which on further hydrolysis gives ethanol. If we want to change the carbon chain length in primary alcohol, the same should be changed in alkyl part of Grignard reagent.

CH₃-Mg-Cl + HCHO → CH₃-CH₂-OMgCl
CH₃-CH₂-OMgCl + H₂O → CH₃-CH₂-OH + MgCl(OH)

Similarly Grignard reagent on reacting with acetaldehyde followed by hydrolysis gives secondary alcohol. For example methyl magnesium chloride reacts with acetaldehyde followed by hydrolysis gives 2-propanol. Grignard reagent on reacting with acetone followed by hydrolysis gives tertiary alcohol.

Nomenclature of Alcohols

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Alcohols are named after the parent alkane chain by replacing ‘ane’ in the parent alkane chain with ‘ol’. For example in CH₃ –OH there is one carbon atom and so the parent alkane name is methane. If we replace ‘ane’ with ‘ol’, we will get methanol. Hence, the compound name is methanol.

If the compound contains branches then the longest chain is selected as parent chain and other alkyl groups are treated as substituents. For example in the following compound the longest chain contains five carbon atoms and hence the compound name is 2 methyl Butanol.

If the compound contains more than two carbon atoms then the position of attachment of OH group should be indicated. For example the following compound is named as 2-Butanol.

In case of compounds containing more than one functional group, the order of priority should be followed. In this halogens will have least priority than alcohols and other functional groups like acids will have more priority than alcohol.

List of Alcohols

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1. Primary alcohol

Here the functional group is attached to a primary carbon atom ( a carbon atom which is connected to exactly one carbon atom). Ethanol is an example for primary alcohol.

2. Secondary alcohol

Here the functional group is attached to a secondary carbon atom which is exactly connected to two carbon atoms. 2-propanol is an secondary alcohol.

3. Tertiary alcohol

Here the functional group is attached to a tertiary carbon atom which is exactly connected to three carbon atoms. 2-methyl-2-propanol is an example for tertiary alcohol.

4. Vinyl alcohol

Iit is an alcohol where the functional group is directly attached to a carbon containing double bond. Prop-1-ene-1-ol is an example for vinyl alcohol.

5. Allyl alcohol

It is an alcohol where the functional group is directly attached to a carbon which is connected to unsaturated carbon. Prop-2-ene-1-ol is an example for allyl alcohol.

6. Benzyl alcohol

Here the functional group is attached to a carbon chain containing the benzene ring. The structure of benzyl alcohol is given below.

7. Dihydric alcohol

The compounds containing two hydroxy group are called as dihydric alcohol.
Ethylene glycol is an example for dihydric alcohol.

8. Trihydric alcohol

The compounds containing three hydroxy group are called as trihydric alcohol.
Glycerol is an example for trihydric alcohol.

Physical Properties of Alcohols

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• Alcohols are colorless liquids with characteristic smell.
• They are high boiling liquids due to presence of hydrogen bonding.
• They are soluble in water.
• Their boiling point increases with increase in the length of carbon chain and increase in the number of hydroxyl groups.
• So, ethylene glycol will have more boiling point that ethanol.

Chemical Properties of Alcohols

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Alcohol are polar molecules due to the presence of OH functional group. The OH functional group can release proton in solution and hence alcohol are slightly acidic.

In the second case the OH functional group can altogether be replaced. So the reaction of alcohols are classified as

1. Reactions involving acidic hydrogen
2. Reactions involving hydroxyl functional group

Reactions of Alcohols

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1. Reaction with sodium

Alcohols react with sodium to give sodium alkoxide and hydrogen. This is the characteristic reaction of alcohol and is often used in organic analysis to identify the alcohol.

2CH₃-CH₂-OH + 2Na → 2CH₃-CH₂-ONa + H₂

2. Reaction with acids (Esterification reaction)

Alcohols condense with acids in the presence of concentrated sulfuric acid to give ester. For example ethyl alcohol condense with acetic acid to give ethyl acetate.

CH₃-CH₂-OH + CH₃-COOH → CH₃-CH₂-O-CO-CH₃ + H₂O

3. Reaction with acidified potassium permanganate (oxidation reaction)

Primary alcohols on oxidation give aldehyde which easily undergoes oxidation to give carboxylic acid with same number of carbon atoms. This is characteristic reaction of primary alcohol as secondary alcohols on oxidation gives ketone which is difficult to oxidize to further.

CH₃-CH₂-OH → CH₃-CHO → CH₃-COOH

4. Reaction with PCl₅, PCl₃, SOCl₂

Alcohols react with chlorinating agents like phosphorus pentachloride, phosphorus trichloride and thionyl chloride to give chloro alkanes.

CH₃-CH₂-OH + PCl₅ → CH₃-CH₂-Cl + POCl₃ + HCl

CH₃-OH + SOCl₂ → CH₃-Cl + SO₂ + HCl

5. Reaction with ammonia

Alcohols react with ammonia to give a mixture of amines. The reaction yields depends on the concentration of ammonia and alcohol.

CH₃-OH + NH₃ → CH₃-NH₂ + H₂O

CH₃-NH₂ + CH₃-OH → CH₃-NH-CH₃ + H₂O

CH₃-NH-CH₃ + CH₃-OH → CH₃-N-(CH₃)₂ + H₂O

6. Dehydration reaction

Alcohols undergo intra-molecular dehydration with concentrated sulfuric acid to give alkene. For example, ethanol on dehydration gives ethene and propanol on dehydration give propene.

CH₃-CH₂-OH → CH₂=CH₂ + H₂O
CH₃-CH₂-CH₂-OH → CH₃-CH=CH₂ + H₂O

At elevated temperature alcohols undergo intermolecular dehydration to give ethers.

CH₃OH + CH₃OH → CH₃-O-CH₃ + H₂O

Alcohol

Alcohols are compounds which has got OH group as their functional group. Alcohols are present naturally in many product like ethanol and methanol.

Alcohols are classified with number of OH groups attached. For example when the alcohol contains only one OH it is called as mono hydric alcohol for example ethanol whose formula is CH₃CH₂OH, when the compound contains two OH group it is called as di hydric alcohol for example as in ethylene glycol CH₂OH-CH₂OH. The alcohol is called as tri hydric alcohol when there is three OH group attached in the compound for example as in glycerol CH₂OH-CHOH-CH₂OH.
Another important way of classifying the alcohol is by the carbon in which the alcohol is attached.

What is Alcohol?

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Alcohol is an organic compound containing hydroxyl functional group. Ethanol a main constituent of beverages and medicines and glycol common antifreeze are some examples of alcohols.

The general formula of alcohol is R-OH, where R can be alkyl group. Depending on the nature of alkyl group (R) the alcohol are classified as primary, secondary, tertiary, vinyl, allyl and benzyl alcohol.

Synthesis of Alcohols

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Alcohols can be synthesized by any of the following ways.

1. By the hydration of alkenes

Alkenes on hydration in the presence of dilute acids give alcohols. For example ethylene on hydration gives ethyl alcohol.

CH₂=CH₂ + H₂O → CH₃-CH₂-OH

Hydration of propene gives 2-propanol in according to Markovnikov's rule. The reaction involves protonation of alkene followed by addition of water.

2. By reduction of aldehydes, ketones, acyl chlorides

Alcohols are synthesized by reduction of aldehyde with lithium aluminum hydride. Reduction of aldehyde generally gives primary alcohols. For example acetaldehyde on reduction gives ethyl alcohol.

CH₃-CHO → CH₃-CH₂-OH

Similarly ketones on reduction give secondary alcohols. For example ketone on reduction gives 2-propanol.

Acyl chlorides like acetyl chloride on strong reduction give alcohols. Acetyl chloride on strong reduction gives ethyl alcohol.

CH₃-COCl → CH₃CHO → CH₃-CH₂-OH

3. By hydrolysis of Grignard reagent

Grignard reagent like methyl magnesium chloride reacts with formaldehyde to give a primary alcohol. Here methyl magnesium chloride reacts with formaldehyde which on further hydrolysis gives ethanol. If we want to change the carbon chain length in primary alcohol, the same should be changed in alkyl part of Grignard reagent.

CH₃-Mg-Cl + HCHO → CH₃-CH₂-OMgCl
CH₃-CH₂-OMgCl + H₂O → CH₃-CH₂-OH + MgCl(OH)

Similarly Grignard reagent on reacting with acetaldehyde followed by hydrolysis gives secondary alcohol. For example methyl magnesium chloride reacts with acetaldehyde followed by hydrolysis gives 2-propanol. Grignard reagent on reacting with acetone followed by hydrolysis gives tertiary alcohol.

Nomenclature of Alcohols

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Alcohols are named after the parent alkane chain by replacing ‘ane’ in the parent alkane chain with ‘ol’. For example in CH₃ –OH there is one carbon atom and so the parent alkane name is methane. If we replace ‘ane’ with ‘ol’, we will get methanol. Hence, the compound name is methanol.

If the compound contains branches then the longest chain is selected as parent chain and other alkyl groups are treated as substituents. For example in the following compound the longest chain contains five carbon atoms and hence the compound name is 2 methyl Butanol.

If the compound contains more than two carbon atoms then the position of attachment of OH group should be indicated. For example the following compound is named as 2-Butanol.

In case of compounds containing more than one functional group, the order of priority should be followed. In this halogens will have least priority than alcohols and other functional groups like acids will have more priority than alcohol.

List of Alcohols

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1. Primary alcohol

Here the functional group is attached to a primary carbon atom ( a carbon atom which is connected to exactly one carbon atom). Ethanol is an example for primary alcohol.

2. Secondary alcohol

Here the functional group is attached to a secondary carbon atom which is exactly connected to two carbon atoms. 2-propanol is an secondary alcohol.

3. Tertiary alcohol

Here the functional group is attached to a tertiary carbon atom which is exactly connected to three carbon atoms. 2-methyl-2-propanol is an example for tertiary alcohol.

4. Vinyl alcohol

Iit is an alcohol where the functional group is directly attached to a carbon containing double bond. Prop-1-ene-1-ol is an example for vinyl alcohol.

5. Allyl alcohol

It is an alcohol where the functional group is directly attached to a carbon which is connected to unsaturated carbon. Prop-2-ene-1-ol is an example for allyl alcohol.

6. Benzyl alcohol

Here the functional group is attached to a carbon chain containing the benzene ring. The structure of benzyl alcohol is given below.

7. Dihydric alcohol

The compounds containing two hydroxy group are called as dihydric alcohol.
Ethylene glycol is an example for dihydric alcohol.

8. Trihydric alcohol

The compounds containing three hydroxy group are called as trihydric alcohol.
Glycerol is an example for trihydric alcohol.

Physical Properties of Alcohols

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• Alcohols are colorless liquids with characteristic smell.
• They are high boiling liquids due to presence of hydrogen bonding.
• They are soluble in water.
• Their boiling point increases with increase in the length of carbon chain and increase in the number of hydroxyl groups.
• So, ethylene glycol will have more boiling point that ethanol.

Chemical Properties of Alcohols

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Alcohol are polar molecules due to the presence of OH functional group. The OH functional group can release proton in solution and hence alcohol are slightly acidic.

In the second case the OH functional group can altogether be replaced. So the reaction of alcohols are classified as

1. Reactions involving acidic hydrogen
2. Reactions involving hydroxyl functional group

Reactions of Alcohols

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1. Reaction with sodium

Alcohols react with sodium to give sodium alkoxide and hydrogen. This is the characteristic reaction of alcohol and is often used in organic analysis to identify the alcohol.

2CH₃-CH₂-OH + 2Na → 2CH₃-CH₂-ONa + H₂

2. Reaction with acids (Esterification reaction)

Alcohols condense with acids in the presence of concentrated sulfuric acid to give ester. For example ethyl alcohol condense with acetic acid to give ethyl acetate.

CH₃-CH₂-OH + CH₃-COOH → CH₃-CH₂-O-CO-CH₃ + H₂O

3. Reaction with acidified potassium permanganate (oxidation reaction)

Primary alcohols on oxidation give aldehyde which easily undergoes oxidation to give carboxylic acid with same number of carbon atoms. This is characteristic reaction of primary alcohol as secondary alcohols on oxidation gives ketone which is difficult to oxidize to further.

CH₃-CH₂-OH → CH₃-CHO → CH₃-COOH

4. Reaction with PCl₅, PCl₃, SOCl₂

Alcohols react with chlorinating agents like phosphorus pentachloride, phosphorus trichloride and thionyl chloride to give chloro alkanes.

CH₃-CH₂-OH + PCl₅ → CH₃-CH₂-Cl + POCl₃ + HCl

CH₃-OH + SOCl₂ → CH₃-Cl + SO₂ + HCl

5. Reaction with ammonia

Alcohols react with ammonia to give a mixture of amines. The reaction yields depends on the concentration of ammonia and alcohol.

CH₃-OH + NH₃ → CH₃-NH₂ + H₂O

CH₃-NH₂ + CH₃-OH → CH₃-NH-CH₃ + H₂O

CH₃-NH-CH₃ + CH₃-OH → CH₃-N-(CH₃)₂ + H₂O

6. Dehydration reaction

Alcohols undergo intra-molecular dehydration with concentrated sulfuric acid to give alkene. For example, ethanol on dehydration gives ethene and propanol on dehydration give propene.

CH₃-CH₂-OH → CH₂=CH₂ + H₂O
CH₃-CH₂-CH₂-OH → CH₃-CH=CH₂ + H₂O

At elevated temperature alcohols undergo intermolecular dehydration to give ethers.

CH₃OH + CH₃OH → CH₃-O-CH₃ + H₂O

Organic Chemistry

The root word of organic chemistry, 'Organic' means that the compounds were synthesized from living organisms in the past. Still now organic chemistry reactions are involving the synthesis of organic compounds from living organism like starch, cellulose etc. Introduction to organic chemistry Organic Chemistry is a sub division of Chemistry study and it deals with the scientific study of structure, properties and the compositions of compounds. This is also considered as the chemistry of carbon containing compounds. Every living organisms, irrespective of plants and animals are composed of organic compounds and anyone with an interest in life would definitely like to know more about the molecules involved in these life processes and also need to have the basic understanding of organic chemistry. What is Organic Chemistry? Organic chemistry is the branch of chemistry dealing with compounds containing carbon-carbon bonds. These carbon compounds are special in nature because most of them covalent in nature and they are highly volatile. As organic compounds have some distinguishing characters they are differentiated from rest of the chemistry and studies separately. The next interesting thing is the number of organic compounds. As carbon can from a long chain due to its catenation ability (an ability to form long chains with itself and with other atoms) it can form many number of compounds. Hence we have to study the properties of organic compounds separately. Organic Chemistry Definition Hence organic chemistry is the branch of chemistry dealing with organic compounds made up of covalent carbon chain. This branch is unique in studying the properties of organic compounds as all of them are covalent and they undergo different set of reactions from Inorganic compounds. Functional Groups in Organic Chemistry One of the special feature of organic chemistry which differentiates it from Inorganic chemistry is the compounds will form a pattern called homologous series. Every organic compound will have a specific part or group where the reactivity is more. This part is called as functional group in the organic compound. All the organic compounds with same functional group will fall under the same homologous series. They will have same chemical properties which make the study of organic chemistry much more easier. For example in the following compounds the hydroxy (-OH) is the functional group and all the compounds are called as alcohols with same physical and chemical properties. The special nature of functional group is all the compounds with same functional group will have same chemical properties. But the physical properties may differ with the number and nature of carbon chain. For example both methanol and butanol will fall under alcohol series. Both will react with sodium to liberate hydrogen gas. 2CH3OH + 2Na → 2CH3ONa + H2 2CH3CH2CH2OH + 2Na → 2CH3CH2CH2ONa + H2 Organic Chemistry Reactions Back to Top Organic chemistry reactions are different from inorganic chemistry reactions. As most of the organic compounds are covalent in nature, the organic chemistry reactions involves the cleavage of the covalent bonds and forming of new bonds. A covalent bond is made up of two electrons and cleavage of such bond may happen in such a way that both the electrons are taken away by one atom resulting in formation of ions. On the other hand the bonding electrons may be equally divided between atom giving rise to free radicals. Hence organic chemistry reactions proceed by the formation of ions or free radicals. 1. Hence the organic chemistry reaction may be classified as Free radical reaction where radicals are formed and initiate the reaction, For example bromination of methane involves formation of bromine free radical to proceed the reaction. Hence the reaction is free radical reaction. CH4 + Br. → CH3Br Nucleophilic reaction where negative ions are produced and attack on positive sides. For example the carbonyl carbon is partially positive charged and negative ions will attack on the carbon easily. Hence all the reactions in aldehyde and ketone are nucleophilic reactions involving negative ions. Electrophilic reaction where positive ions are produced and attack on negative sides. For example benzene ring is a rich source of Π electrons. Hence all the reactions will proceed with the attack of this electron by positively charged ions. Hence all the reactions in the benzene ring are electrophilic reactions. 2. The organic chemistry reactions may also further divided as Addition reaction: where an atom or group is added across an unsaturated bond. For example addition of bromine with ethylene gives di-bromo ethane. CH2=CH2 + Br2 → CH2Br-CH2Br Elimination reaction: where a molecule is eliminated from an organic compound to give unsaturated compound. For example ethyl bromide on elimination in the presence of alcoholic KOH gives ethene. CH3-CH2-Br → CH2=CH2 + HBr Oxidation reaction: It is the type of reaction where oxygen is added or hydrogen is removed from an organic compound. For example ethyl alcohol on strong oxidation in the presence of acidified potassium permanganate gives acetic acid. Reduction reaction: It is the type of reaction where oxygen is removed or hydrogen is added to an organic compound. For example acetone on reduction with lithium aluminium hydride gives 2-propanol. Condensation reaction: It is the type of reaction where two organic compounds combine together to give one compound by elimination of simple molecules like water, HCl etc. For example condensation of acid and alcohol gives ester. CH3-CH2-OH + CH3COOH → CH3CH2OCOCH3 + H2O Polymerization reaction: It is the reaction in which small organic molecules called as monomers combined together to give a large chain of macro molecule called as polymer. Polymerization of vinyl chloride gives polyvinyl chloride, shortly called as PVC. Substitution reaction: It is the reaction in which an atom or group is replaced by another atom or group in organic compound. For example chloromethane reacts with potassium hydroxide to give methanol and potassium chloride. CH3-Cl + KOH → CH3OH + KCl