KINETIC EFFECTS INDUCED BY CELLULOSE ON WATER-CATALYZED REACTIONS - HYDROLYSIS OF 2,4-DINITROPHENYL CELLULOSE XANTHATE AND SOME SUGAR XANTHATE ESTER ANALOGS

The hydrolysis of 2,4-dinitrophenyl cellulose xanthate (CelXDNP) was s tudied in 10% v/v aqueous ethanol at 25 degrees C and mu = 0.1 (KCl). The water-catalyzed hydrolysis showed that, as for p-nitrobenzyl cellu lose xanthate, it occurs through two parallel reactions with rate cons tants k'(H2O) = 4.40 x 10(-3) s(-1) for the fast hydrolysis, and k ''( H2O) = 6.90 x 10(-5) s(-1) for the slow hydrolysis. The entropy of act ivation of the fast hydrolysis was 0.7 +/- 1.8 cal K-1 mol(-1). Extern al nucleophiles such as hydroxide and simple amines show simple first- order kinetics. The spontaneous hydrolysis of CelXDNP in acetone-water mixtures indicates that the fast reaction does not occur through wate r polymers and that for water molarity higher than 30 M there are no a cetone molecules (or very few) in the highly ordered cybotactic region of cellulose. The spontaneous hydrolysis of methyl 4,6-O-benzylidene- alpha-D-glucopyranoside 3-(S-p-nitrobenzyl-xanthate) although is faste r than the G-isomer, it is slower than the fast hydrolysis of p-nitrob enzyl cellulose xanthate (CelXNB). Also Delta S-not equal is highly ne gative (-41.0 cal K-1 mol(-1)), as it is for alkyl and sugar analogues . Only for the fast hydrolyses of CelXDNP and CelXNB is the entropy of activation almost zero. It is concluded that there is no neighbouring OH effect on the fast hydrolysis of cellulose xanthate esters.