UNSATURATED ALCOHOLS 10$ 



Unsaturated Fatty Acids. 



These acids contain in their molecule one or more pairs of their 

 carbon atoms linked together by a double bond. Unsaturated acids 

 containing a triple bond. are also known. 



Acrylic acid is the simplest and first member of the homologous 

 series of Unsaturated acids containing one double bond. It was first 

 obtained by the oxidation of acrolein with silver oxide, but is more 

 readily prepared by the reactions described for obtaining unsaturated 

 hydrocarbons (p. 54) from /3-bromopropionic acid. 



Acrylic acid is a liquid with a pungent smell and boils at 140. 



The next member is crotonic acid y CH 3 . CH=CH . COOH. 



Crotonic acid is a solid which melts at 72. 



Okie acid, which contains 18 carbon atoms and the double bond 

 in the middle of the chain, is present in combination with glycerol in 

 animal and vegetable fats from which it is prepared (p. 99). 



Oleic acid at the ordinary temperature is a colourless, oily liquid 

 of sp. gr. -900 at 1 1 '8 with neither smell nor taste. It oxidises very 

 readily in the air, becoming brown, acid in reaction and rancid in 

 smell. It can be frozen to a white crystalline solid which melts at 14. 

 It cannot be distilled at the ordinary temperature, but at 10 mm. pres- 

 sure it distils at 223 and it is volatile with superheated steam. 



Linoleic acid also contains 18 carbon atoms, but two double bonds. 

 It is contained in linseed and other oils. 



Linoleic acid resembles oleic acid, but is more readily oxidised by 

 the oxygen of the air. It is owing to its presence and that of other 

 more unsaturated acids in linseed, cotton seed and rape seed oils that 

 these oils possess the property of forming the so-called " drying oils". 

 Oxygen is absorbed and transparent resinous substances are formed. 



The salts of the unsaturated fatty acids are more soluble than those 

 of the saturated fatty acids. The lead and mercury salts of oleic acid 

 are soluble in ether and are used for separating the mixture of acids 

 obtained from fats. 



Owing to the presence of the double bonds the unsaturated acids 

 combine by addition with the halogens, halogen acids, etc., and reduce 

 permanganate solution becoming oxidised ; thus 



If a solution of oleic acid in chloroform be treated with bromine 

 dissolved in chloroform, or iodine dissolved in chloroform containing 

 also mercuric chloride, the colour of the halogen is discharged until 

 the acid is completely saturated by absorption of the halogen. 



If a solution of sodium oleate be poured into a solution of potassium 

 permanganate, the colour of the permanganate disappears and man- 

 ganese dioxide separates out. 



