+2 UNIT 13 PAGE- 3
SOME COMMERCIALLY IMPORTANT COMPOUNDS
1. Methanol
Methanol , CH3OH , also known as ‘wood alcohol’ can be produced by destructive distillation of wood. Today , most of methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature in presence of Cu-ZnO-Cr2O3 catalyst.
Methanol is a colourless liquid with boiling point 337 K. It is highly poisonous in nature. Ingestion of even small quantities of methanol can cause blindness and large quantities , even death. Methanol is used as a solvent in paints, varnishes and chiefly for making formaldehyde, which in turn is used as a preservative for biological specimen and for making synthetic resins.
Ethanol
Fermentation
Ethanol is manufactured by fermentation of starch or sugar. Fermentation is a process in which complex organic compounds are broken down into simpler molecules by the action of biological catalysts known as enzymes. Enzymes are complex organic compounds which act as catalysts in reaction taking place in living organisms. These are called bio-catalysts.
i) Ethanol from sugar solution(molasses). Molasses is the mother liquor left after the removal of sugar from sugar cane juice. It still contains 50% sugar. This is then diluted to about 10% concentration of sugar. Then, calculated amount of yeast is added at about 298 K. Yeast supplies the enzymes invertase and zymase which are essential for fermentation. These enzymes convert sugar ultimately into ethanol. In this process about 8-10% solution of ethanol, called ‘wash’ is obtained. Further dehydration with quick lime and distilling with sodium or calcium gives a 99.8% ethanol sample.
ii) Ethanol From starch : Ethanol is also prepared industrially from starchy materials like potato, yam, etc. Starchy materials are made into a paste by heating with super heated steam at about 335 K and malt is added. The malt contains the enzyme diastase which converts starch into maltose.
The product obtained is cooled to about 305 K and yeast is added. It gives enzyme maltase which converts maltose to glucose.
The enzyme zymase also provided by yeast converts glucose into ethanol.
Ethanol is a colourless liquid bp 351 K. It is used as a solvent in paint industry and in the preparation of a number of carbon compounds. The commercial alcohol is made unfit for drinking by mixing it some copper sulphate (to give it a colour) and pyridine (a foul smelling liquid). It is known as denaturation of alcohol.
Nowadays , large quantities of ethanol are obtained by the hydration of ethene.
Ethane-1,2-diol (Ethylene glycol)
Methods of Preparation
1. From ethene : Ethylene glycol is prepared by the oxidation of ethylene using dilute alkaline potassium permanganate solution (Bayer's reagent).
2. On a commercial scale, ethylene glycol is prepared by passing ethylene through hypochlorous acid (HCℓO). The chlorohydrin formed is hydrolysed with sodium bicarbonate to form glycol.
3. It can also be prepared on a commercial scale by the hydrolysis of ethylene oxide with dil. Hydrochloric acid. Etylene oxide is obtained by passing a mixture of etylene and air over silver catalyst at 470-670 K.
Physical properties
Glycol is a colourless , syrupy liquid with sweet taste.
Its melting point is 261.5 K and boiling point 470 K.
It is highly soluble in ethanol and water due to the presence of hydrogen bonding.
Chemical properties
The molecule of glycol has two alcoholic groups. It gives all the characteristic reactions of primary alcohols. In addition , it gives some characteristic reactions. In most of its reactions, the two hydroxyl groups are attacked one after the other.
1. Action of sodium : Monosodium glycollate is obtained when glycol is treated with sodium at 320 K while disodium derivative is obtained at 430 K.
2. Action of Hydrogen chloride : Hydrogen chloride converts glycol into ethylene chlorohydrin at 430 K whereas ethylene chloride is formed at 470 K.
3. Action of phosphorus pentachloride and Thionyl chloride : Ethylene chloride is formed.
4. Oxidation : Ethylene glycol on oxidation with different oxidising agents give different products.
i) With dil. HNO3 or alkaline KMnO4 , it gives oxalic acid.
ii) When periodic acid (HIO4) or lead tetra-acetate is used, carbon-carbon bond undergoes cleavage and formaldehyde is formed.
iii) When acidified KMnO4 or acidified K2Cr2O7 is used, carbon-carbon bond undergoes cleavage and formic acid is formed.
iv) Oxidation with HIO4 - Glycollic cleavage : 1,2-Glycols or vic-glycols (having -OH on adjacent carbon atoms) are oxidised by periodic acid with breaking of bond in between the carbon atoms bearing the -OH groups. The O-H bearing carbon atoms in the vic-glycols are converted into carbonyl compounds (aldehydes or ketones) . Only vicinal glycols are oxidised by HIO4. Ethylene glycol gives two molecules of formaldehyde.
HIO4 ® HIO3 + [O]
This oxidation reaction may be used :-
To distinguish vic. Glycols from polymethylene glycol by identifying the carbonyl compounds.
To determine the structure of glycol by identifying the carbonyl compounds.
To determine the number of adjacent -OH group pairs from the number of HIO4 molecules consumed.
5. Pinacol rearrangement : Pinacol is ditertiary 1,2-Glycol and tetramethyl ethylene glycol is the simplest pinacol. When pinacol is heated with dilute mineral acid, it gets dehydrated to a ketone called pinacolone with a molecular rearrangement.
This type of rearrangement is called pinacol rearrangement.
Ethylene glycol also undergoes this type of rearrangement on heating with dilute mineral acid under pressure giving acetaldehyde.
V) Dehydration : Under different conditions , ethylene glycol undergoes dehydration in different ways :
When heated alone at 775 K, it forms ethylene oxide,
In the presence of anhydrous ZnCl2, ethylene glycol on heating gives acetaldehyde.
On heating with Con. H2SO4, ethylene glycol gives dioxane.
Uses of ethylene glycol
It is used in the manufacture of dacron, dioxane, ethylene oxide, etc.
It is used as an anti-freeze in car radiators.
It is used as a solvent.
In organic synthesis.
Propane-1,2,3-triol (GLYCEROL )
Glycerol or glycerine is present in oils and fats as its carboxylic esters. Oils and fats are triesters of glycerol with higher fatty acids like palmitic acid stearic acid, etc. These esters are commonly known as glycerides.
PREPARATION
1. From oils and fats : Glycerol is prepared on a large scale as a by-product in the manufacture of soap. Soaps are manufactured by boiling oils and fats with 10% caustic alkali solution. The reaction is called saponification reaction.
The soap is salted out (or precipitated) by adding sodium chloride to the reaction product. The filtrate obtained after filtering out the soap is known as spent lye. It contains approximately 3-5% glycerol besides water, soluble soap, sodium chloride, unused alkali, fatty and proteineous matter.
The spent lye is then allowed to settle in a tank where most of the suspended impurities settle down. The clear solution is decanted to another tank, where it is treated with dilute hydrochloric acid to neutralise most of the free alkali. It is then treated with alum or aluminium sulphate along with steam. The remaining free alkali is precipitated as aluminium hydroxide and the soluble soaps are converted to insoluble aluminium soaps. These impurities are filtered off. The filtrate is then concentrated under vaccum when most of the sodium chloride separates out. This is filtered and the filtrate is treated with animal charcoal to remove undesirable colour. After filtration, it is again subjected to vaccum distillation. The glycerol, thus obtained is approximately 90-95 % pure. To obtain pure glycerol, it is re-distilled under reduced pressure till a distillate of specific gravity 1.26 is obtained.
2. From Propylene : Glycerol is prepared on a large scale from propylene. Propylene is chlorinated at 753 to 773 K to give allyl chloride. This is hydrolysed to allyl alcohol by reacting with sodium carbonate solution under pressure. The allyl alcohol is treated with chlorine water (hypochlorous acid) and subsequently hydrolysed to obtain glycerol.
Physical properties of Glycerol
Glycerol is a colourless liquid.
It has a sweet taste and its sweetness is comparable to that of sugar.
Glycerol is non-toxic in nature.
It is miscible with water in all proportions.
Glycerol is hygroscopic in nature and absorbs moisture from air.
Glycerol has a very high boiling point (563 K) because of strong hydrogen bonding in the molecule. The melting point of glycerol is 290 K.
Chemical properties
Glycerol contains two types of -OH groups, i.e., primary and secondary alcoholic group. It undergoes all reactions characteristic of these groups. In addition, it also undergoes some reactions typical of polyhydric alcohols. Some important reactions of glycerol are :
1. Oxidation : The oxidation of glycerol gives a variety of products depending upon the nature of oxidising agent used. For example,
(a) With mild oxidising agents like bromine water and hydrogen peroxide in the presence of ferrous sulphate(Fenton's reagent) , glycerol is oxidised to a mixture of glyceraldehyde and dihydroxyacetone.
(b) With dilute nitric acid, glycerol gets oxidised to a mixture of glyceric acid and tartronic acid.
With concentrated nitric acid , the main product is glyceric acid.
(c) When heated with periodic acid, glycerol undergoes oxidative cleavage giving formaldehyde and formic acid. The periodic acid is reduced to iodic acid.
Note
When adjacent -OH group pairs are present , the middle OH bearing carbon is oxidised to a carboxylic acid.
(d) Strong oxidising agents like warm acidified potassium permanganate oxidises glycerol to a mixture of oxalic acid, carbon dioxide etc.
2. Dehydration : On heating with potassium hydrogen sulphate, glycerol undergoes dehydration to acrolein which is an unsaturated aldehyde with an offensive odour.
The dehydration can also be effected by Con. H2SO4 or P2O5.
3. Reduction with HI acid : When glycerol is warmed with small amount of HI, glycerol tri-iodide is formed. This being unstable splits into allyl iodide and finally to propene. However, with excess of HI , propylene produced adds on a molecule of HI to give isopropyl iodide (2-Iodopropane).
4. Nitration : Glycerol reacts with a mixture of con HNO3 and H2SO4 at 283-298 K to form glyceryl trinitrate (Nitroglycerine).
Nitroglycerine is a highly explosive substance. A mixture of glyceryl trinitrate and glyceryl dinitrate adsorbed on kieselguhr ( a kind of porous earth) is called dynamite. Dynamite was discovered by Alfred Nobel. Dynamite is used for rock blasting and for making bombs.
5. Reaction with sodium : At room temperature, sodium reacts with one of the primary -OH groups of glycerol to form monosodium derivative. However, at higher temperature(373 K) both the primary groups react to form di-sodium derivative. Secondary -OH group does not react with sodium.
6. Reaction with oxalic acid : Glycerol on heating with oxalic acid at 383 K forms glycerol monoformate which on hydrolysis produces formic acid.
Glycerol on heating with oxalic acid at 503 K gives allyl alcohol as the product.
Uses of glycerol
1. As a sweetening agent in confectionary and beverages.
In the manufacture of nitroglycerine which is used as an
explosive.
3. As an antifreeze in automobiles.
4. As a lubricant for watches and clocks.
It is used in the manufacture of glyptal resins.
In the manufacture of cosmetics and transparent soaps.
Phenol
1. From Cumene : Cumene is oxidised by air to cumene hydroperoxide, which on treatment with dil. Sulphuric acid gives phenol and acetone.
2. From Benzene (Raschig process) : Vapours of hydrochloric acid are passed over benzene at 500 K in the presence of cupric chloride and excess of air to form chlorobenzene. Steam is then passed through chlorobenzene at 800 K in the presence of silica as catalyst to yield phenol. The method is known as Raschig's process.
Phenol , mp 314 K is moderately soluble in water (8% at 298 K). It is a strong antiseptic. It is widely used as a raw material for the manufacture of important dyes , drugs and pharmaceuticals, polymers and a number of organic chemicals.
Ethers
The chemically unreactive nature, solvent properties and low cost of ethoxyethane make it the most important of the simple ethers. It is used as a solvent for oils, gums, resins, etc. Ethoxyethane has also been widely used as an inhalation anaesthetic. However, because of its slow effect unpleasant recovery period, other compounds such as ethrane and isoflurane have replaced ethoxyethane as an anaesthetic. Phenyl ether , is used as a heat transfer medium because of its high boiling point, 531 K
A number of naturally occuring phenols and ethers , particularly ring substituted anisoles are used as flavourings and in perfumes because of their pleasant odour. Anethole- a constituent of anaise seed , eugenol – present in oil of cloves, vanillin –present in oil of vanilla bean and thymol – present in thyme and mint are examples of phenols and ethers that are used in perfumes and in flavourings.
PROBLEMS
01. Give the equations of the following reactions :
reaction of propene with mercuric acetate followed by hydrolysis.
Oxidation of propan-1-ol with alkaline KMnO4.
Reaction of bromine in CS2 with phenol
Action of dilute HNO3 with phenol
Treating phenol with chloroform in presence of aqueous NaOH at 343 K.
02. How much bromine (in moles) is needed to produce 2,4,6- Tribromophenol from 1 mole of phenol ?
03. Arrange the following in the increasing order of boiling points:
CH3CH2CH2CH2Br
ii) CH3CH2CH2CH2OH
iii) CH3CH(OH)CH2CH2OH
iv) CH3CH(Cl)CH3
04. Give the structures of products in the following reactions:-
Nitration of bromobenzene
ii) Sulphonation of phenol
iii) Phenol with aqueous bromine
iv) Phenol with dil. Nitric acid.
Chlorobenzene with NaOH at high temperature and pressure.
05. How will you distinguish between :
Benzyl alcohol and phenol.
Ethyl alcohol and benzyl alcohol.
n-Propanol and iso-propanol.
sec-butanol and tert-butyl alcohol.
06. Bring out the following conversions :-
Acetaldehyde to isopropyl alcohol.
Ethanol to chloroform.
Acetic acid to ethanol.
Ethanol to acetic acid.
Formaldehyde to methanol
Acetaldehyde to ethanol.
Ethyl alcohol to propionic acid.
Methanol to ethanol.
2-Propanol to 1-Bromopropane.
Acetone to tert-Butyl alcohol.
Ethene to ethanol.
Formaldehyde to ethanol.
07. Predict X, Y, Z in the following sequence of reactions :
08. A compound A gives positive Lucas test in 5 minutes. When 6 g of A is treated with sodium metal, 1120 ml of hydrogen is evolved at STP. Assuming A to contain one atom of oxygen per molecule, write the structural formula of the compound A. Compound A when treated with PBr3 gives compound B which when treated with benzene in presence of anhydrous aluminium chloride gives compound C. Write the structural formula of B and C.
09. A chloro compound A showed the following properties
Decolourised Br2 in CCl4
Absorbed hydrogen catalytically
Gave a precipitate with ammoniacal cuprous chloride.
When vapourised 1.49 g of A gave 448 ml of vapour at STP. Identify A and write down the equations of reaction at step (iii).
10. How will you convert :
Chlorobenzene to benzene
b) Benzene to resorcinol
c) Chlorobenzene to benzoic acid
d) Benzene to phenol.
e) Phenol to benzoic acid.
11. Convert :
i) Ethyl chloride to propionic acid
Ethylene to n-Propyl alcohol.
12. How are the following conversions carried out ?
propene to propan-2-ol
Benzyl chloride to benzyl alcohol
Ethyl magnesium chloride to propan-1-ol
Methyl magnesium bromide to 2-methylpropan-2-ol
13. How will you prepare butan-1-ol from:
1-Bromobutane
a suitable alkene
14. Name the reagents used in the following reactions
oxidation of a primary alcohol to carboxylic acid
oxidation of a primary alcohol to an aldehyde
bromination of phenol to 2,4,6-tribromophenol
benzyl alcohol to benzoic acid
dehydration of propan-2-ol to propene
butan-2-one to butan-2-ol
15. How is ethane-1,2-diol prepared from
ethylene oxide
ethene
1,2-dibromoethane
16. Give the IUPAC names of the following ethers (N268)
(a) CH3OCH2CH(CH3)CH3
(b) CH3CH2CH2OCH3
CH3OCH2CH2Cl
O2NC6H4OCH3(p)
17. Write the names of reagents and equations for the preparation of following ethers by Williamson synthesis.
1-Propoxypropane
methoxybenzene
2-methyl-2-methoxypropane
1-methoxyethane
QUESTIONS
Distinguish between alkyl and aryl halides.
What are gem dihalides and vic-dihalides ?
Whare halogen derivatives ? Classify them into mono-, di- , tri- and tetrahalogen derivatives. Give specific illustrative examples.
Give the IUPAC names and structural formulae of the following :
Isobutyl bromide b) Tertiary butyl chloride
ortho bromo toluene d) Isopropyl bromide
e) Benzyl chloride f) m-Chlorotoluene
Write the possible structural isomers of C4H9Br.
Write the structural formulae of mono-halogen substituted derivatives of n-butane.
Write all possible structures for a compound having molecular formula C3H7Cl.
Write the IUPAC names of all the isomers of butyl bromide.
What are primary, secondary and tertiary alcohols ?
Give the general methods of preparation of alkyl halides.
How are alkyl halides prepared in the laboratory ?
Give the general methods of preparation of aryl halides.
Give a method of preparation of sec-butyl chloride.
Show, giving equations, how chlorobenzene can be prepared from aniline.
Write some important properties of alkyl halides.
How will you convert :
Chlorobenzene into toluene
b) Benzene diazonium chloride into chlorobenzene
c) Benzene to chlorobenzene
d) n-Propyl bromide into iso-propyl bromide
e) Methyl bromide to ethyl bromide
Ethyl bromide to methyl bromide.
g) Trichloro acetone to chloroform
h) Ethyl chloride to propionic acid.
Isopropyl chloride into n-propyl chloride.
2-Chlorobutane into 2-butanol.
k) 2-Chlorobutane to 2-butanol.
l) Methyl iodide to nitromethane
m) Propyl chloride into propyl amine.
How is iodoform prepared from propanone ? Give its reaction sequence.
What do you understand by :
Nucleophilic substitution
ii) Electrophilic substitution ?
The boiling point of ethyl bromide is higher than that of ethyl chloride. Account for it.
Treatment of alkyl chloride with aqueous KOH leads to the formation of an alcohol. Account for it.
How do the boiling points of alkyl halides containing the same alkyl group vary and why ?
Justify the following and write the chemical equation for each :
Nitration of benzene is a electrophilic substitution reaction.
The reaction of alkyl halide with silver nitrite is nucleophilic substitution reaction.
The C-X bond in aryl halides is shorter in comparison to alkyl halides. Explain.
Why are dehydrating conditions used in the reaction of an alcohol with a halogen acid ?
Account for the following observations :
Alcohols do not react with NaBr, but form alkyl bromides when a mixture of NaBr and H2SO4 is used.
Alkyl halide is hydrolysed to alcohol slowly, but the reaction is rapid when KI is added to reaction mixture.
Although alkyl halides are polar, yet they are insoluble in water. Explain why ?
Why is the halogen atom of an alkyl halide readily substituted by an other group ?
Secondary alkyl halides are more reactive than primary alkyl halides and tertiary alkyl halides are more reactive than secondary ones. Explain why ?
In what main respect does chlorobenzene differ from benzyl chloride ?
Which is the heaviest alkyl halide and why ?
Iodoform gives a yellow precipitate with silver nitrate on heating, but chloroform does not. Explain.
Why is chloroform kept in dark bottles ?
How do you distinguish between chlorobenzene and methyl chloride ?
Give one chemical test to distinguish between ethyl bromide and bromobenzene.
How would you distinguish between chlorobenzene and benzyl chloride ?
How will you distinguish between CH2=CHCH2Br and CH3CH2CH2Br ?
How will you distinguish between chlorobenzene and propyl chloride ?
How will you distinguish between n-propyl bromide and 3-bromo-1-propene ?
Give a suitable test to distinguish between benzyl chloride and benzyk bromide ?
Write notes on : I) Carbyl amine test ii) Iodoform test.
Give the general methods of preparation of monohydric alcohols.
Describe one industrial method for the preparation of methanol.
Give the uses f methanol and ethanol.
Describe one industrial method for the preparation of ethanol.
What is fermentation ?
What is meant by : (1) Absolute alcohol (2) Denatured spirit (3) Methylated spirit
Discuss the chemical properties of alcohols.
Explain with equations, the reaction of sulphuric acid with ethyl alcohol under different conditions.
Mention industrial uses of ethanol.
Write a note on Lucas test for hydroxyl group in alcohols.
Write equations for reactions which takes place when 1-propanol is treated with :
excess HBr under reflux
Small amount of Con. Sulphuric acid.
Acidified KMnO4.
ethanoic acid in presence of con. Sulphuric acid.
v) Thionyl chloride.
Give reactions which distinguish between primary, secondary and tertiary alcohols.
Why are the boiling points of alcohols higher than those of the corresponding alkanes and haloalkanes ?
Why are lower alcohols soluble on water; while the higher alcohols are not ?
Account for the following :
Ethanol has a higher boiling point than the corresponding alkane, ethane.
Boiling points of monohydric alcohols increases with increase in carbon atoms.
Describe methods for preparation of phenol.
How is phenol prepared commercially ?
Describe the preparation of phenol from chlorobenzene.
Describe the important reactions of phenol.
Mention the industrial uses of phenol.
Which of the two phenol and methanol is acidic and why ?
Phenol is acidic, while methanol is neutral. Explain.
How do you account for the acidic character of phenol ?
Why are the boiling points of phenols higher than the corresponding aromatic hydrocarbons ?
Account for the following :
In reactions involving cleavage of carbon-oxygen bond of alcohols, some acid is added to facilitate the reaction.
Phenols do not undergo substitution at C-OH bond.
If an alcohol is treated with excess of sulphuric acid, no esterification takes place.
What are glycerides ? How is glycerol obtained commercially
What happens when glycerol reacts with :
potassium bisulphite ii) HI iii) periodic acid
What are glycols ? How is ethylene glycol prepared ? Give its uses.
Why is glycerol more viscous than ethanol ?
Describe the important uses of glycerol.
Mention the important property to glycerol which is useful in cosmetics.
Describe the following :
Nitration of glycerol
oxidation of oxalic acid with potassium permanganate.
Write notes on :
Kolbe's reaction ii) Reimer-Tiemann reaction
What happens when :
Methanol reacts with C2H5MgX ?
Sodium phenoxide reacts with carbon dioxide at 400 K
and 4-7 atm pressure.
Glycerol reacts with excess of HI ?
Ethanol reacts with Con. H2SO4 at 425 K ?
Glycerol reacts with oxalic acid at 383 K ?
Glycerol reacts with HNO3 / H2SO4 ?
How will you distinguish between ethanol and methanol ?
Bring out the following conversions :
Phenol to 2,4,6-tribromophenol.
Cane sugar to ethyl alcohol.
Sodium benzenesuphonate to phenol.
Glycerol to allyl iodide
phenol to p-hydroxyazobenzene.
Glycerol to acrolein
phenol to picric acid.
Phenol to salicylic acid.
phenol to benzene.
Salicylic acid to aspirin
phenol to toluene
Salicylic acid to salol
Benzyl alcohol to toluene.
) Toluene to benzyl chloride
Allyl alcohol to glycerol.
Phenol to acetophenone
Acetone to iodoform
Formaldehyde to n-butane
Ethyl alcohol to glycol
Ethylene to 2-Propanol.
How is phenol obtained from aniline and converted into 2-hydroxy benzoic acid ?
Give reasons :
Chloroform is chlorine compound, but it does not give white precipitate with silver nitrate solution.
Nitration of phenol gives ortho and para-products only.
What is an ambidant nucleophile ? Explain with a suitable example.
How will you convert : a) Ethanol to acetone
Formaldehyde to n-butane.