Dialkyl sulphate

FS(0)20CH3. Colourless liquid, b.p. 94°C. Functions as a powerful methylating agent, even for amides and nitriles which are not attacked by conventional alkylating agents like dialkyl sulphates. 

By the action of a dialkyl sulphate upon a Grignard reagent, for example CsH.CHjCl-1-Mg CeH.CHjMgCl C,H,CHjMgCl -1- (C,Hj),SO, — CeHjCH.CH.CH, MgCl(SOAH )... 

By the action of a dialkyl sulphate upon a Grignard reagent, for example ... 

Anomeric alkylation has been extensively studied by Schmidt and co-workers,62 and the main alkylating agents used were dialkyl sulphates, benzyl bromide, allyl bromide63 or various O-triflates, allowing the synthesis of disaccharides.64 The stereochemical outcome of anomeric alkylation is known to depend on many parameters such as the base, the solvent and its effect on solubility and concentration, the temperature, chelation effects, presence of additives, and nature of the electrophilic species.62 65... 

The same object is attained by treating alkali salts with a dialkyl sulphate. Usually in this case only one alkyl group takes part in the reaction in accordance with the equation ... 

In other reactions also the OH-group of the phenols shows itself to be more reactive than that of the aliphatic alcohols. Phenols, but not alcohols, react easily with diazomethane. With other alkylating agents also, such as alkyl halides, and dialkyl sulphates, the phenols react even in aqueous alkaline solution whilst the alcohols do not react under such conditions. Benzoyl derivatives, most of which crystallise readily, are excellently adapted for the characterisation of phenols (Schotten-Baumann reaction). 

The catalysed two-phase alkylation of carboxamides has the advantages of speed and simplicity over the traditional procedures and provides a valuable route to secondary and tertiary amines by hydrolysis or reduction of the amides, respectively. The procedure appears to be limited, however, to reactions with primary haloalkanes and dialkyl sulphates, as secondary haloalkanes are totally unreactive [6, 7]. The use of iodoalkanes should be avoided, on account of the inhibiting effect of the released iodide ion on the catalyst. Also, the A-alkylation reaction is generally susceptible to steric effects, as seen by the low yields in the A -cthylation of (V-/-butylacetamide and of A-ethylpivalamide [6]. However, the low steric demand of the formyl group permits A,A-dialkylation and it is possible to obtain, after hydrolysis in 60% ethanolic sulphuric acid, the secondary amines having one (or, in some cases, two) bulky substituent(s) [7]. 

Simple alkylations of carboxylate anions, by such alkylating agents as alkyl halides, dialkyl sulphates, and quaternary ammonium compounds, are generally straightforward SN2 reactions, and will not be discussed here. 

Typical synthetic procedures include the reaction of alkyl halides with the silver salts of carboxylic acids, the reaction of carboxylate anions in alkali with an excess of a dialkyl sulphate, (especially dimethyl sulphate), and heating tertiary184 or quaternary ammonium salts of carboxylic acids. These routes are particularly valuable for the preparation of esters of seriously sterically hindered acids. For example, Fuson et al.iK made the methyl ester of 2,4,6-triethylbenzoic acid by heating the tetramethyl ammonium salt to 200-250°C, viz. 

The diselenides, RSe.SeR, are prepared by the interaction of potassium diselenide and dialkyl sulphates or alkyl halides ... 

Note.—Dialkyl sulphates are extremely poisonous on no account must their vapour be inhaled. Work with them should be carried out in a good fume cupboard they must be added to mixtures from a tap funnel, for if spilled on the hands they are absorbed through the skin. Should any fall on the clothes, these must be changed at once. See also p. 261. 

For this reason the arylsulphonate esters find use as alkylating agents (cf. dimethyl sulphate and dialkyl sulphates, Section 4.2.24, p. 430). 

The hydrolysis of methyl fluoride in water (Glew and Moelwyn-Hughes, 1952) requires more negative values of AO and AS than that of the other methyl halides (see also Chapman and Levy, 1952) but the comparison requires extrapolation over a large temperature interval and may therefore not be reliable (see SectionIIB2). The reactions of methyl nitrate (McKinley-McKee and Moelwyn-Hughes, 1952) and dialkyl sulphates (Robertson, 1966) with water show values of AG and AS which are similar to those found in the Su2 solvolysis of halides. 

New reactions of various phosphazenes with a wide range of electrophilic species continue to be reported. These include those of alkoxy-derivatives with dialkyl sulphates, e.g. to give (56), or with sulphenyl chlorides, e.g. the reaction that produces (57) (see Scheme 4). With pyridine, compound (56) can be converted into two isomeric products (58) and (59). 

In (6.267) the by-prodnct ethyl bromide may compete with the butyl bromide to form some EtPO (OEO2. Other alkyl derivatives such as dialkyl sulphates or alkyl p-toluene sulphonates may also be used for this reaction. 

In the Michaelis reaction (which usually gives lower yields than the corresponding Arbusov reaction), a metal dialkylphosphite (dialkylphosphonate - see below) is reacted with an alkyl halide to give a dialkyl ester of an alkyl phosphonate (6.272). Alkyl p-toluene sulphonates or dialkyl sulphates may be used in place of alkyl halides. Esters of unsaturated phosphonic acids, containing OH and CO groups can be obtained from an unsaturated aldehyde and a dialkyl phosphite (6.273). 

An important feature of sulphation chemistry is the thermal instability of the "acid sulphate", which breaks down to a mixture of products including the parent alcohol, the dialkyl sulphate (ROSO2OR), the dialkyl ether (ROR), isomeric alcohols, olefins (R CH=CH2> and esters (ROSO3R). Because of the thermal instability of the "acid sulphate" it is necessary to avoid high sulphation temperatures and to neutralise the acid sulphation product soon after its formation. An ageing time of about 1 minute at 30-50°C is adequate for the second reaction where the desired alkyl hydrogen sulphate is formed. In practice the minimum sulphation temperature feasible is determined by the need for the feedstock and reaction mixture to be mobile liquids. 

Useful methods for specific 2-0 or 4-0 methylations (or ethylations) of tetronic acids have been published (Scheme 20). °" The more reactive -oxygen can be alkylated by treatment with dialkyl sulphates under a variety of conditions whereas preparation of the 2-O-alkyl derivative requires prior acylation of the 4-oxygen, followed by alkylation using trialkyloxonium salts (see ref. 148). Some very interesting chemistry has been evolved during efforts towards a total... 

The adduct (31) formed from dialkyl sulphates and DMF is a potent esteri-fying agent for a range of carboxylic acids. Carbon dioxide-catalysed ester exchange has been described. Carboxylic acids react readily with diphenyl disulphide in the presence of triphenylphosphine to afford the corresponding phenyl thioesters. ... 

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