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GATE PSU

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For

GATE Syllabus

Revised Study

Material

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TABLE OF CONTENTS

Chapter 1

INORGANIC CHEMICALS

2 2 2 2 3 3 5 5 5 6 7 8 9 10 10 12 13 13 13 14 14 15 16

Chapter 2

FERTILIZERS

18 18 18 19 19 22
22
23
23
28
29
29
29
29
30
31
31
33
33

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Chapter 3

NATURAL PRODUCTS

34
34
34
34
35
35
35
35
36
37
37
37
37
38
38
38
39
40
40
40
42
42
42
49
54

Chapter 4

PETRO CHEMICALS

56
56
56
58
60
62

Chapter 5

POLYMERS

64
64
69
70
71
71
71
71
72
72

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73
74
74
74
75
76
79
80
81
82
82
83
83
83
84
84
85
86
89
91
92

Chapter 6

SYNTHETIC ORGANIC CHEMICALS

97
97
97
98
100
101

Ȃ102

105
108
111
111
112
112
113

Chapter 7

CEMENT TECHNOLOGY

115
115
115
115
115
116
116

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117
117
117
117
117
118
118
119
119
119
119
120
123
124
125
125

Chapter 8

LEVEL 1

127

LEVEL 2 138

Chapter 9

UNSOLVED QUESTIONS

150

Chapter 10

QUESTIONS (2004 TO 2015)

153
153
155
157
159
161
163
164
166
168
170
171
172

Chapter 11

SOLUTIONS

174

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3.1 INTRODUCTION

Nature synthesizes many organic compounds starting basically from the CO2˛O2 photosynthesis process. The principal industries based on natural products are:

Oil And Fats

Pulp And Paper

Sugar

3.2 OIL AND FATS

There are following points to remember:

ƒ Oils and fats are trimesters of higher fatty acids with glycerol, i.e. they are glycerol esters and glycerides. They are called triglycerides or triglycerols. ƒ Oils are liquids at ordinary temperature and their molecules are basically glyceryl esters of unsaturated fatty acids. The molecules of fats are basically glyceryl esters of saturated fatty acids. ƒ The fatty acids have un-branched carbon chain and their molecules normally contain even number of carbon atoms. The most abundantly occurring fatty acid in nature is palmitic acid. ƒ The glycerides in which all the three fatty acids are identical are called simple triglycerides. The glycerides in which the three fatty acid units are not identical are called mixed triglycerides. The mixed triglycerides more commonly occur in nature than the simple triglycerides.

CHAPTER

3

NATURAL PRODUCTS

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3.2.1 METHODS OF EXTRACTION OF OILS AND FATS

Oils and fats can be extracted by using any of the following methods:

3.2.1.1 RENDERING

The animal tissues containing fat are heated with water, so that the fat melts and get separated out.

3.2.1.2 PRESSING

The plant seeds containing oil are crushed by rollers and then pressed under hydraulic press, so that the oils get separated out. The remaining pressed cake is used as fodder for the milch cows, buffalos etc.

3.2.1.3 SOLVENT EXTRACTION

The oils and fats are soluble in common organic solvents, like petroleum ether benzene, CS2 etc. Therefore, oils and fats left behind in the pressed cake can be completely extracted out by using the above solvents. The crude oils separated by the above methods are washed with a small amount of alkali solution due to which free acids and colloidal impurities are removed. After that, the oil is subjected to bleaching by animal charcoal at about 75 ˛ 80 0C. in the end, steam is passed through the oil for removing adhering and soluble impurities.

3.2.2 CLASSIFICATION OF OILS AND FATS

Oils can be classified as follows:

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Oils

Vegetable oils Animal oils

(Olive oil, unsaturated oil, etc.) (Whale oil, cod liver oil, etc.) Drying oils Semi ˛ drying oils Non ˛ drying oils

Fats can be classified as follows:

Fats

Vegetable fats Animal fats

(vegetable ghee, coconut oil, etc.) (Desi ghee, lard, etc.)

Drying oils Non ˛ drying oils

3.2.2.1 VEGETABLE OILS

DRYING OILS

Drying oils readily dry up on exposure to air. These are commonly used in paints and varnishes. The important example of drying oils is linseed oil.

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SEMI DRYING OILS

Semi drying oils dry up very slowly on exposure to air. These are also commonly used in paints and varnishes.

E.g. Cottonseed oil.

NON DRYING OILS

Non drying oils do not dry up even on exposure to air. e.g. til oil and mustard oil. Cholesterol (C27H46O), which is a very important animal lipid, is structurally not a fat. It is an unsaturated alicylic alcohol, which form rhombic plants, melting point 148 0C. Phytosterol is a plant lipid, which forms needle like crystal, melting point 132 ˛ 144 0C.

3.2.3 PHYSICAL PROPERTIES

ƒ In pure form, these are tasteless, colorless and odorless liquids or solids. ƒ These are lighter than water and immiscible with water. ƒ These are soluble in petroleum ether, benzene, ether, chloroform, acetone, CS2, etc.

ƒ These are neutral.

ƒ These from emulsions on stirring with emulsifiers, like soaps, gelatins, etc.

3.2.4 REACTIONS

3.2.4.1 HYDROLYSIS

The oils and fats undergo hydrolysis by water or dilute acids to give a mixture of glycerol and fatty acids (aliphatic mono-carboxylic acids).

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The mother liquor left behind after removal of the fatty acids is called sweet water,

Which is used for the manufacture of glycerol.

When caustic alkalis are used for the hydrolysis of oils and fats, then glycerol and soaps (alkali metal salts of higher fatty acids) are formed. This reaction is called saponification.

Glyceride + 3NaOH Glycerol + 3R COONa (Soap)

Enzymes can also bring about the hydrolysis of oils and fats. e.g. emulsion of oils or fats undergoes complete hydrolysis in three or four days to give glycerol and fatty acids on using the enzyme, lipase. The fatty acids are obtained in sufficiently pure form by this method.

3.2.4.2 HYDROGENATION

The oils are liquids at ordinary temperatures, because they are glyceryl trimesters of higher unsaturated fatty acids. In order to convert the oils (liquids) into fats (solids), the oils are subjected to hydrogenation under pressure in the presence of finely divided nickel catalyst. This process results in saturation of the double bonds present in the fatty acid units to form single bonds by addition of hydrogen. e.g. the oil triolein (a liquid having b.p. 170C) on hydrogenation gives a fat tristearin (a solid having melting point 60 0C). The above process of hydrogenation is called hardening of oils and is used in the manufacture of vegetable ghee and margarine.

3.2.4.3 HYDROGENOLYSIS

When excess amount of hydrogen is passed through an oil or a fat, then glycerol and higher alcohols are obtained. The breaking up of an organic molecule by excess of hydrogen is called Hydrogenolysis. e.g. tristearin undergoes Hydrogenolysis to give glycerol and octadecyl alcohol.

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26

17 35 2Tristearin Glycerol + C H CH OH (Octadecyl alcohol)H

3.2.4.4 RANCIDIFICATION

When an oil or a fat is kept exposed to air and humidity for a very long period of time, then it (especially fat) starts giving an unpleasant smell. This change is called rancidification and it involves oxidation and hydrolysis. Oxidation at the double bond results in the formation of aldehydes, which undergo oxidation to form lower fatty acids. The unpleasant taste and smell is actually due to these acids and aldehydes. Pure oils and fats can be stored in good condition when they are kept away from air and humidity.

3.2.5 USES

ƒ As important food materials.

ƒ In the manufacture of soaps, candles and glycerol.

ƒ As lubricants.

ƒ In the manufacture of paints and varnishes.

ƒ As illuminants.

ƒ As medicines. E.g. croton oil and castor oil are used as purgatives.

3.2.6 MANUFACTURE OF VEGETABLE GHEE

HYDROGENATION OF OILS

Oils are liquids at ordinary temperature, because unsaturated glycerides are present in them in high amounts. Therefore, in order to convert them to fats (solids at ordinary temperature), they are subjected to hydrogenation under pressure in the presence of finely divided nickel catalyst. Thus, solid saturated glycerides, i.e., fats are obtained. This process is called hydrogenation of oils or hardening of oils. Manufacture of vegetable oil involves the following steps.

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(i) SEPARATION OF FREE ACIDS: The oil first heated and a calculated amount of NaOH is added to it, so that the free acids undergo neutralization. The salts and suspended impurities so formed get separated out in the form of scum. (ii) BLEACHING: The oil filled in one tank is then decanted out to the other tank. The oil is bleached or decolorized at 75 ˛ 80 0C with the help of animal charcoal and then filtered. (iii) DEODORISATION: In order to deodorize the oil, superheated steam is passed through it. (iv) HYDROGENATION:quotesdbs_dbs5.pdfusesText_10

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