Sulphonate esters protonation

The Neber rearrangement of oxime sulphonate esters (equation 28) is a useful method for the synthesis of a-aminoketones78. The reaction is base catalysed and involves abstraction of the most acidic proton a to the oxime functional group, as exemplified by the exclusive formation of compound 40 in this rearrangement (equation 29). 

Protonation of sulphonate esters in aqueous sulphuric acid mixtures appears to increase the rates of S l reactions in solvent compositions of about 60% w/w or more, although the extent of protonation of substrates was estimated to be only 1% (increasing, but still less than 30% protonation, in 98% sulphuric acid)10. Solvolyses of primary alkyl sulphonates have been examined in sulphuric acid and in fluorosulphuric acid, containing 1M potassium fluorosulphate130,131 under these conditions, it was roughly estimated130 that ethyl tosylate would be only about 0.1% protonated. 

General base catalysed halogenation of carbon acids often involves a rate-determining proton transfer from carbon, and halogenation is a technique which is frequently used for obtaining rates of proton transfer. The technique has been developed particularly by Bell [34] to measure rates of proton transfer from ketones. Other carbon acids have been studied, however, for example, esters [35], sulphonates [36], nitro-paraffins [37], and cyanocarbons [38]. Under chosen conditions which may vary depending upon the substrate, the mechanism, illustrated for acetone in eqns. (19) and (20),... 

In the presence of oxidizing agents (e.g. sodium metaperiodate, hydrogen peroxide, m-chloroperbenzoic acid, t-butyl-hypochlorite, iodobenzene dichloride, etc.) both penicillins and cephalosporins undergo facile oxidation to either sulphoxides or sulphones. The esters of penicillin sulphox-ides (4) were described in 1949 [1]. It was found later [5] that the free acids could be oxidized by periodate. When a 6(7)-/3-acylamino side-chain is present in the molecule the resulting reagent-approach control due to the N-H proton promotes the formation of the (S)-sulphoxide (4a) [6,7]. 

Fischer-Speier esterification to give a salt of an amino acid ester (by refluxing an alkanol with anhydrous HC1 or hot benzyl alcohol with toluene-/>-sulphonic acid) is straightforward. The fact that the nearby amino group is protonated when the carboxy group reacts to give a-amino acid esters does not slow the reaction down unduly a nearby positive site might have been expected to reduce the electrophilic character of the carboxy carbon atom. Without an acid catalyst, Walkylation can accompany esterification (Equation 4.6). 

Acylphosphonic acids (1-oxoalkylphosphonic acids) and their dialkyl esters undergo acid-catalyzed fission with the formation of carboxylic acids (or their alkyl esters) using a suiphonic acid as the catalyst the formation of an alkyl carboxylace is accompanied by that of an alkyl sulphonate. The reaction may be visualized as occurring through protonation on the carbonyl oxygen and migration of an alkoxy group from phosphorus... 

Several compounds have been prepared by nucleophilic substitution of chlorine in 2-chloro-l,3-dithian with Grignard reagent (RMgBr), malonic esters, and phenols.A mechanism for the de-ethoxycarbonylation of the 2-(l,3-dithianyl)malonates by sodium chloride or sodium ethoxide has been studied. 2-Chlorotetrahydrofuran reacts with nucleophiles such as 2-lithio-2-phenyl-l,3-dithian (326) by three simultaneous mechanisms i.e. substitution, proton abstraction, and electron transfer) to give the products (327)—(330) (Scheme 12)/° When a dithian (331 R = H or COiMe) was treated with a sulphonyl chloride in pyridine, ring-expansion to the 5//-l,4-dithiepin (332) occurred instead of the expected formation of a sulphonate. ... 

Dimethylcyclo-octa-1,5-diene reacts with boron trifluoride diethyl etherate to give 2,5-dimethylbicyclo[3,3,0]oct-2-ene (60%), whereas l,5-dimethylbicyclo[3,2,l] octan-8-ol (156 R = H 50%) and its tosylate (156 R = Ts 70%) are formed on treatment with perchloric acid-aqueous dioxan and toluene-p-sulphonic acid, respectively. Preliminary results indicate that cis,ci -cyclo-octa-l,5-diene and hydrogen peroxide-mercury(ii) nitrate react to give a transannular peroxide. The boron trifluoride diethyl etherate-benzene catalysed cyclizations of the cyclo-octenyl ester (157 R = COjEt) and ketone (157 R = COMe) to the bicyclo[3,3,l]nonanes (158 R = C02Et) and (158 R = COMe), respectively, have been studied further. Possible intermediates in these reactions were synthesized but no cyclized products were obtained. The mechanism that was finally suggested involves protonation of the... 

The amount of alkali needed to saponify the sulphonated and unsulphonated esters in 1 g of sample is equal to the amount of acid needed to protonate the —COO groups produced by saponification of the esters,... 

Poly(ethylene terephthalate) is most usually encountered in the crystalline form and, as such, it is soluble at normal temperatures only in proton donors which are capable of interaction with the ester group. Effective solvents of this kind are chlorinated and fluorinated acetic acids, phenols and anhydrous hydrofluoric acid. The polymer is soluble at elevated temperatures in various organic liquids, which include anisole, aromatic ketones, dibutyl phthalate and dimethyl sulphone. Chloroform has the peculiar property of dissolving amorphous poly(ethylene terephthalate) at temperatures below 0°C,but on warming such solutions the polymer separates in crystalline form. Chloroform is without effect on polymer which has already been crystallized. 

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