n6 CHEMICAL PROPERTIES AND COMPOSITION 



Consider finally bodies containing carboxyl, in which the 

 facility for introducing metal in the hydroxyl group, is 

 again increased by the presence of the new atom of oxygen 

 in the carboxyl group 



= C O-H. 



The acid character thus arising changes markedly in 

 strength under the influence of the combined hydrogen, and 

 in the sense expected. As previously (Part I, p. 135) the 

 dissociation constant may be taken as a measure of the 

 strength ; we then get in the extreme cases 



Benzoic acid C 6 H 5 COOH K = 0-006, 

 Heptylic acid C 6 H 13 COOH K < 0-00145, 



whilst for valerianic acid (C 5 H 10 OJ K = o-ooi6i, and for 

 hexylic acid (C G H 12 O 2 ) 0-00145. 



(/3) Hydrogen intensifies basicity. Since basic character 

 is due to the possibility of forming hydroxyl ions, the 

 property of hydrogen in question can only be studied in 

 organic compounds of a basic character, i.e. the alcohols. 

 Actually it appears that the tendency of alcohols to esteri- 

 fication, in which their basic character is shown, is modified 

 in the expected manner by hydrogen. Again, taking extreme 

 cases, and choosing as appropriate measure of the tendency to 

 esterification not the velocity but the limit reached we have 



C 6 H 5 OH 8-6% C H 13 OH 67.3 '/,, 



i.e. phenol heated to 144 for a sufficient time with the 

 equivalent amount of acetic acid combined to the extent of 

 9 per cent., but primary normal hexyl alcohol to the extent 

 of 67 per cent. 



It is possible to go further in this case, with the aid of 

 the more complete investigation of Menschutkin, and not 

 only to demonstrate the influence of hydrogen in general, 

 but to show that the hydrogen which is nearest to the 

 hydroxyl group is the most effective ; the average limit 

 was found to be for 



H 3 COH XH 2 COH YXHCOH ZYXCOH 

 70 67 60 10%, 



