The kinetics of the reaction of cyclopentanol with PhNCO or OCN(Cd-In)NCO was studied in toluene, di-n-butyl ether and acetonitrile. The results suggest a predominant influence of the aggregation state of alcohol.

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The dependence of the reaction rate of cyclopentanol with phenyl isocyanate on the concentration of monomeric alcohol [1] in toluene, di-n-butyl ether and acetonitrile suggests a reaction scheme involving various complexes.

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In this paper, the kinetics of the reaction of phenylisocyanate with cyclopentanol, catalyzed by di(n-butyl)tin di-(2-ethylhexanoate) (DBTDEH), was studied at different temperatures in the same solvents as previously [1], i.e in acetonitrile (ACN), di-(n-butyl)ether (DBE) and toluene (Tol), in order to determine the Arrhenius energy, which is shown to be larger in the presence of the tin(IV) catalyst than in its absence [2], and the apparent activation entropy, which was derived from the values of the extrapolated intercepts of the In k-//7"graphs. The results demonstrate that entropic configurational effects are the prevailing cause of the accelerating effect of the tin(IV) catalyst on this reaction.

The pseudo-first order kinetics of the reaction of cyclopentanol with phenylisocyanate, catalyzed by dibutyltin di(2-ethylhexanoate) (DBTDEH), was studied by means of UV and IR spectrophotometry. Reaction orders with respect to catalyst and to monomeric alcohol [1] were considered in toluene (Tol), di(nbutyl)ether (DBE) and acetonitrile (ACN). The results, which were interpreted with the aid of rate equations previously derived [2-4] on the basis of a reaction scheme involving an alkoxytin(IV) intermediate, indicate that pre-reaction complexes of solvent-dependent composition are formed in the rate determining step of both catalyzed and uncatalyzed mechanisms [5], INTRODUCTIONPrior studies related to the organotin-catalyzed nucleophilic addition of alcohol in excess to isocyanate have shown that this reaction is first order in isocyanate. The so obtained pseudo-first order rate constants do not vary linearly with the concentration of alcohol or of catalyst. Various kinetic behaviours were reported. For Borkent [6] the order is close to 0.5 in catalyst and results from the presence of a cationic active intermediate R 3 Sn + while for Van der Weij [7] the value 0.5 found with respect to both catalyst and alcohol reflects the formation of an ionizable alcohol-catalyst complex. Such interpretations are questionable since these reactions are also easy in apolar solvents. For Entelis et al.[8] a ceiling of the rate, observed at high alcohol and catalyst concentrations, should be due to a partial blocking of reacting species by nonproductive reactant(s)-catalyst homo-and/or heteroassociates. Bloodworth and Davies [9], considering the high reactivity of tin alkoxides towards isocyanate, suggested the tin carboxylate to be partly alcoholyzed to an active alkoxytin catalyst (scheme 1). This type of reaction scheme is also supported by some of our experiments dealing with the decelerating effect exerted by carboxylic acids or thiols [2,3], However, in the former works, the order was generally determined with respect to the overall alcohol content. The molecular meaning of the found values is questionable since associated OH groups exhibit a much smaller reactivity than free ones, so that any interpretation of the kinetic influence of alcohol must logically take into account its solvent-dependent sharing among free and associated forms [1],