Disparate Behavior of Carbonyl and Thiocarbonyl Compounds: Acyl Chlorides vs Thiocarbonyl Chlorides and Isocyanates vs Isothiocyanates

Abstract

The reaction of benzoyl chloride with methanol catalyzed by pyridine is 9 times more rapid than is the same reaction with thiobenzoyl chloride. The difference in reactivity, as well as the dealkylation reactions that occur when the reaction of thiobenzoyl chloride is catalyzed by bases such as Et 3 N, can be understood in terms of the charge distributions in the intermediate acylammonium ions. The reaction of PhNCO with ethanol occurs at a much higher rate (4.8 × 10 4 ) than that of PhNCS, corresponding to a difference in activation free energies for the additions of 6 kcal/mol. Transition states for each of these reactions were located, and each involves two alcohol molecules in a hydrogen

Computational study on vapor phase coupling reaction between diiso(thio)cyanates with diamines, diols, and dithiols

“…In comparison, isothiocyanate had a larger E a than isocyanate by 8.6 ± 11.1 kJ/mol, with ethane‐1,2‐diiso(thio)cyanate as the only exception. The slower reaction of isothiocyanates toward alcoholysis than isocyanates has been observed experimentally, and is associated with a reduced positive charge of the thiocarbonyl C atom . In our calculations, the NPA charges of the C atoms belonging to the NCX groups of (IB, IE, ITB, ITE) are (0.917, 0.909, 0.274, 0.278), respectively; in other words, it is confirmed that the atomic charge of C atoms belonging to NCS are less positive than those of NCO.…”

A comparison of some properties of C=O and C=S bonds

“…Benzoyl chloride has been found to be nine times more reactive toward methanol than thiobenzoyl chloride. 4 The reactions of phenoxycarbonyl chloride and phenoxythiocarbonyl chloride with trifluoromethyl phenyl carbinol in the presence of triethylamine has been examined, 5 and whereas the carbonyl chloride reacts normally with the intermediate acylammonium ion to give the ester, the thiocarbonyl chloride reaction occurs by nucleophilic attack at an ethyl on the N in the thioacylammonium ion, leading to a thioamide as the product. Phenylisocyanate reacts with cyclohexanol with 5 mol% N-methylimidazole as the catalyst to give a carbamate within 24 hr, but phenylisothiocyanate gives no product under these conditions.…”

“…Phenylisocyanate reacts with cyclohexanol with 5 mol% N-methylimidazole as the catalyst to give a carbamate within 24 hr, but phenylisothiocyanate gives no product under these conditions. 4 The rate of the uncatalyzed reaction of phenylisocyanate with ethanol proceeds 48,000 times as fast as the corresponding reaction of phenylisothiocyanate. 4 We have explored some of these differences, both experimentally and computationally, in order to learn more about the origin of the differences.…”

“…4 The rate of the uncatalyzed reaction of phenylisocyanate with ethanol proceeds 48,000 times as fast as the corresponding reaction of phenylisothiocyanate. 4 We have explored some of these differences, both experimentally and computationally, in order to learn more about the origin of the differences. In this report, we will be concerned with the differences in physical properties of compounds with C=O and C=S groups.…”

Inner Workings of a Cinchona Alkaloid Catalyzed Oxa‐Michael Cyclization: Evidence for a Concerted Hydrogen‐Bond‐Network Mechanism

“…The result18 was k H / k D =1.4, which may appear low for a reaction with a hydrogen transfer in the rate‐determining step. However, the value is in the expected range for a concerted addition reaction, approaching a reverse E1cb‐type mechanism,43, 45, 46 or related 6‐membered cyclic transition states involving two hydrogen‐bond donors 39c. A similar primary deuterium KIE of 1.61 has been obtained for the crotonase‐catalyzed (enoyl‐CoA hydratase) hydration, which proceeds by a concerted, stereospecific syn addition of water to an unsaturated CoAS‐ester 47.…”