New Chlorocarbonates Derived From Aromatic and Dihydroxy Alcohols

Oesper, Ralph E.; Broker, Walter; Cook, Walter A.

doi:10.1021/ja01687a028

Cited by 16 publications

(6 citation statements)

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“…Many tertiary amines can be used as acid acceptors for the preparation of aryl chloroformates (45,529). Amines of the dimethylaniline type gave the best results with this procedure, probably because of their low reactivity toward the chloroformates.…”

Section: Methods Of Synthesis Of Chloroformatesmentioning

confidence: 99%

The Chemistry of Chloroformates

Matzner¹,

Kurkjy²,

Cotter³

1964

Chem. Rev.

139

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Section: Methods Of Synthesis Of Chloroformatesmentioning

confidence: 99%

The Chemistry of Chloroformates

Matzner¹,

Kurkjy²,

Cotter³

1964

Chem. Rev.

139

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“…The reaction mechanism can be determined on the basis of the Brønsted dependence of log k OH 1 or log k d Ј from Table 1 on the change in pK a P of the leaving phenol (Eqns 3, 4). ( (5) In order to roughly estimate the extent to which the proton is removed from N-H and O-H groups, we adopted the value of the ρ constant of ionisation of substituted carbamates 1 to the first degree (ρ = 0.13) and that of ionisation of substituted phenyl N-methoxycarbamates, which possess only one acidic proton N-H (ρ = 0.83). 3 The large difference between the two constants is due also to the fact that during the dissociation of the N-H bond, the negative charge is nearer to the substituent.…”

Section: Mechanism Of Base-catalysed Degradation Of Substituted Pheny...mentioning

confidence: 99%

Kinetics and mechanism of base-catalysed degradations of substituted aryl-N-hydroxycarbamates, their N-methyl and N-phenyl analogues

et al. 2004

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The kinetics and mechanism of the degradation reactions of substituted phenyl N-hydroxycarbamates and their N-methyl and N-phenyl analogues have been studied at pseudo-first-order reaction conditions in aqueous buffers and sodium hydroxide solutions at 20 [degree]C and 60 [degree]C and at I= 1 mol[middle dot]l(-1). The dependence of log k(obs) on pH for phenyl N-hydroxycarbamates at pH < 9 and pH > 13 is linear with the unit slope; at pH 10-12 log k(obs) is pH independent. The Bronsted coefficient [small beta](lg) is about -1 (pH 7-13) and -1.53 (pH > 13) indicating that the degradation reaction of phenyl N-hydroxycarbamates follows an E1cB mechanism giving the corresponding phenol/phenolate and HO-N[double bond, length as m-dash]C[double bond, length as m-dash]O. The latter species undergoes further decomposition to give carbonate, nitrogen and ammonia as final products. In contrast to the phenyl N-hydroxycarbamates the N-methyl derivatives at pH 7-9 undergo degradation to the corresponding phenol/phenolate, carbonate and methylamine via a concerted mechanism ([small beta](lg) is about -0.75). The only exception is 4-nitrophenyl N-hydroxy-N-methylcarbamate in which the predominant break down pathway proceeds via the Smiles rearrangement to give sodium N-methyl-(4-nitrophenoxy)carbamate. At pH > 9 the reaction of N-hydroxy-N-methylcarbamates is kinetically complex: the dependence of absorbance on time is not exponential and it proceeds as a consecutive two-step reaction. N-Hydroxy-N-phenylcarbamate under the same conditions undergoes degradation to phenol, carbonate, aniline and azoxybenzene.

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“…Dioxan was refluxed over sodium wire under nitrogen until the metal surface was bright and then distilled. The substituted phenyl chloroformates were prepared by a literature method 28 and are all known comp o u n d ~. ~~ Sodium azide (0.65 g) dissolved in the minimum quantity of 10% aqueous dioxan was added slowly to a stirred solution of freshly distilled phenyl chloroformate (1-36 g) in dioxan (25 ml).…”

Section: Methodsmentioning

confidence: 99%

Kinetics and mechanism of the base-catalysed hydrolysis of some substituted phenyl chloroformates

Butler¹,

Robertson²,

Bacaloglu³

1974

J. Chem. Soc., Perkin Trans. 2

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A study of kinetic isotope effects and activation parameters indicates that, in the hydrolysis of phenyl chloroformate, acetate ion and pyridine act as nucleophilic catalysts. Both the spontaneous and pyridine catalysed hydrolyses of substituted phenyl chloroformates fit a Hammett plot. The effect of solvent polarity and added salt indicates that there is little charge separation in'the transition state for hydrolysis. The mechanism of reaction is discussed.THERE have been numerous investigations of basecatalysed ester hydrolysis but the reactions o f chloroformates, which have a carbonyl group more susceptible to attack than that of normal esters, have not been studied in such detail. The present paper reports a kinetic investigation of this reaction. RESULTS AND DISCUSSIONAlkyl chloroformates undergo spontaneous hydrolysis in water and there is a change of mechanism from S32 to Sxl along the series methyl, ethyl, propyl, and i~opropyl.~ The evidence for this comes from a determination of the values of A H t , AS$, and AC,, which show variations associated with a change of mechanism. For the hydrolysis of phenyl chloroformate all the evidence favours an S N ~ mechanism but the rate-determining step may be formation of the tetrahedral intermediate or loss of chloride ion.for such a change in the reaction of substituted anilines with ethyl chloroformate from a plot of AH$ against AS: (which gives two, distinct, parallel lines) and from a Hammett plot using 0-constants. Electron-withdrawing substituents give a line of slope 1-57 and electron-donating groups one with slope 5.56. In a previous study of the hydrolysis of substituted phenyl chloroformates in aqueous acetone, elect ron-donating substit uents were found not to fall on a linear Hammett plot using 0 or 0-constants, and this could be interpreted in terms of a change of mechanism. However, all the other evidence (entropy-enthalpy correlations, kinetic isotope effects, and solvents effects) is against a change of mechanism.To study this matter further we determined the rate of spontaneous hydrolysis of substituted phenyl chloroformates in aqueous dioxan by monitoring the appearance of the substituted phenol spectroscopically.* The results obtained give a single, linear relationship between log Kobs and the Hammett ci constants, with substituents ranging from P-methoxy to $-nitro (Figure 1). The correlation coefficient Y for this line is 0.991, and so there is no evidence for a change of mechanism. The fact that there is correlation with 0 rather than c-constants indicates that there is little anionic character in the

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New Chlorocarbonates Derived From Aromatic and Dihydroxy Alcohols

Cited by 16 publications

References 0 publications

The Chemistry of Chloroformates

The Chemistry of Chloroformates

Kinetics and mechanism of base-catalysed degradations of substituted aryl-N-hydroxycarbamates, their N-methyl and N-phenyl analogues

Kinetics and mechanism of the base-catalysed hydrolysis of some substituted phenyl chloroformates

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