Correlation of the rates of solvolysis of acetyl chloride and α-substituted derivatives

Abstract

Additional specific rates of solvolysis have been determined for acetyl chloride and diphenylacetyl chloride. These are combined with literature values to carry out correlation analyses, using the extended Grunwald–Winstein equation with incorporation of literature values for solvent nucleophilicity (NT) and solvent ionizing power (YCl). Parallel analysis are carried out using literature values for the specific rates of solvolysis of trimethylacetyl chloride, chloroacetyl chloride, phenylacetyl chloride, and α-methoxy-α-trifluoromethylphenylacetyl chloride (MTPAC). Chloroacetyl chloride and MTPAC react by an addition-elimination pathway, with the addition step rate-determining, over the full range of solvents. Acetyl chloride reacts over the full range of solvents by an ionization pathway, with considerable nucleophilic solvation. The other three substrates can solvolyze with the domination of either mechanism, depending on the properties of the solvent. Reports concerning the use of product selectivity values, kinetic solvent isotope effects, and computational studies as additional probes of the mechanism of solvolysis are discussed.Key words: Grunwald-Winstein equation, acyl chlorides, mechanism of solvolysis, solvent nucleophilicity.

Kinetic Studies that Evaluate the Solvolytic Mechanisms of Allyl and Vinyl Chloroformate Esters

“…In just the seven TFE (aq) and HFIP (aq) mixtures, we obtain 0.93 ± 0.12, 0.66 ± 0.14, −0.84 ± 0.30, 0.974, and 36 for l , m , c , R , and F respectively. This l / m ratio of 1.41 obtained for the TFE and HFIP mixtures is similar in magnitude to that previously observed for the solvolyses of acetyl chloride ( l / m ratio of 1.19) [74] and 4-morpholinecarbonyl [75] chloride ( l / m ratio of 1.12). Such ranges in l / m ratios were reported to articulate unimolecular ionization (S N 1) pathways with considerable nucleophilic solvation at the developing carbocation [74,75].…”

“…A substrate concentration of approximately 0.005 M in a variety of solvents was employed. The rate constants for the slow solvolytic reactions were determined by the trimetric method [23] and the faster rates were followed by conductance, at appropriate time intervals [74]. For some of the runs, calculation of the specific rates of solvolysis (first-order rate coefficients) was carried out by a process in which the conventional Guggenheim treatment [76] was modified [77] so as to give an estimate of the infinity titer, which was then used to calculate for each run a series of integrated rate coefficients.…”

Evaluation of Methylthio and Phenylthio Group Effects in the Solvolyses of 2-Chloro-2-(methylthio)acetone and 2-Chloro-2-(phenylthio)acetophenone Using Extended Grunwald-Winstein Equations

“…More recently, our results 4 for the study of solvolyses of chloroacetyl chloride, the "parent" phenylacetyl chloride and α-methoxy-α-trifluorophenylacetyl chloride, 5 with on the α-carbon powerfully electron withdrawing [methoxy (-OCH 3 ) and trifluoromethyl (-OCF 3 )] groups, in aqueous organic solvents including fluorinated solvent systems also showed different reaction channels, determined by the neighboring groups. Much faster (~10 6 times) specific rates of solvolysis of chloroglyoxalate esters (ROCOCOCl), with the insertion of a carbonyl (C=O) group, were observed relative to those of corresponding ROCOCl solvolyses.…”

Correlation of the rates of solvolysis of α-bromoisobutyrophenone using both simple and extended forms of the Grunwald-Winstein equation and the application of correlation analysis to related studies

“…The extended Grunwald-Winstein equation [3-6], which has been found to be very useful in its application to the specific rates of solvolysis of a wide variety of substrates, such as phosphorus compounds [34], silicon compounds [35], acid chlorides [36], chloroformate esters [37], chlorothioformate esters [38], and heterocyclic compounds [39], is here applied to the solvolyses of tertiary alpha-substituted ketones, some of which have, contrary to earlier opinions summarized elsewhere [12], been found to be capable of forming carbocations with the charge formally adjacent to the carbonyl group under solvolytic conditions [10-12]. …”