CONSTITUENTS OF THE BIOSPHERE 



11 



(d) Dibasic and Polybasic Acids 



These play an important part in the chemistry of Hfe. Present in small 

 amounts in animal tissues and bacteria they are present in quantity in 

 vegetable tissues. In both cases they have very important functions. 



Only one 1:2 diacid is possible, oxalic acid COOH.COOH, an acid 

 which is readily oxidized by permanganate to COo and water. The simplest 

 1:3 diacid is malonic acid COOH.CHg.COOH, which decomposes at 

 100°C into acetic acid and COo. The 1:4 diacids are represented by 

 succinic acid COOH.CH2.CH2.COOH. Heat causes their dehydration to 

 form an internal anhydride. 



CH.— COOH 



CH,— CO 



^ H0O + 



CH2— COOH 



Succinic acid 



\ 



o 



/ 



CH2— CO 



Succinic anhydride 



Fumaric acid COOH.CH : CH.COOH, heated at 140X in a closed vessel 

 with a little water, is changed into its isomer maleic acid. 



H— C— COOH H— C— COOH 



I! I! 



H— C— COOH COOH— CH 



Maleic acid Fumaric acid 



{e) Hydroxy-acids 



Lactic acid CH3CHOH.COOH is one of the acids most commonly 

 found in nature. When a hydroxy-acid is heated it readily loses water, but 

 the course of the reaction differs according to the relative positions of the 

 carboxyl and hydroxyl groups. If the two groups are in the 1, 2 position, 

 as in lactic acid, thev will from a laciide 



R 



I 

 CH 



I 

 COO 



OH 



H 



OOC 



R 



2H2O + CH— O CO 



H 



HO 



HC 



R 



CO — O — CH 



R 



If the carboxyl and hydroxyl groups are in the 1, 3 position then heating 

 will produce an unsaturated acid : 



CH2OH— CH2— COOH 



CHo=CH— COOH+HoO 



