Pure Dimethylformamide Research Articles

Base-catalysed mutarotation of glucose in dimethylformamide and dimethyl sulphoxide

The rate of mutarotation of glucose has been measured in pure dimethylformamide and dimethyl sulphoxide with substituted benzoate ions as catalysts, and in 80 vol % dimethyl sulphoxide-water with acetate and chloroacetate as catalysts. Unlike many other base–catalysed reactions in these solvents, the rates show no subtantial increase over those observed in water. This is interpreted in terms of a strong involvement of water with the transition state in aqueous media, in accordance with earlier suggestions concerning the mechanism of related reactions such as the addition of water and alcohols to carbonyl compounds. In combination with previously reported pK values in the appropriate solvents, the results show that there is a good correlation of the catalytic effect of the anion bases with their basic strengths. The observed Bronsted coefficients are slightly higher (β= 0.6 in dimethylformamide and dimethyl sulphoxide) than in water (β= 0.4).

Synthesis of tetraarylphosphonium salts under ullmann reaction conditions

Various arylation reactions of triphenylphosphine (1) are known which lead to tetraarylphosphonium salts [1-3]. We have found that on boiling (I) with iodobenzene in pure dimethylformamide (DMF) in the presence of metallic copper and CuI (reaction i) the double salt of tetraphenylphosphonium (II) iodide and cuprous io,lide is formed in 44% yield and with mp 216-219~ Found: C 43.80; H 3.40%. C24H20PCuI 2. Calculated: C 43.89; H 3.08%, other salts of (II) were also prepared from the double salt; iodide, mp 332334~ Similarly prepared was the cupriiedide of p-tolyltriphenylphosphonium, the yield was 13% with mp 186-186.5~ Found: C 44.42; N 3.76. C25H22!PCuI2 . Calculated: C 44.77; H 3.31% and its fluoborate, mp 204-205~ From reaction (i) in the absence of DMF or CuI, with other coilditions remaining the same, only traces of the salts of the substances were isolated, in the absence of copper the yield of (II) was halved. The yield of (II) was also clearly decreased in impure DMF. It is assumed that the reaction under study involves the intermediate formation of the arylcopper which then achieves a radical arylation of triphenyiphosphine within the complex of the latter with the aryleopper and cuprous :iodide.

A comparison of the alkali methoxides in the high-frequency titration of acids in dimethylformamide

The five alkali-methoxides were prepared and standardized in 9 : 1 benzene-methanol solution. The strengths of these bases were compared by means of HF response and conductance curves and by means of the titration of a selected series of acids dissolved in dimethylformamide. The caesium and rubidium methoxides were the strongest bases. However the difference in basicity of these two methoxides as compared to potassium and sodium methoxide does not warrant their preferred use. Lithium methoxide acted as a very weak base in the 9 : 1 benzene-methanol solvent but became more dissociated as the concentration of the methanoi was increased. There was a small but definite drift of the Oscillometer as the concentration of the methoxide ion was increased. This was shown to be due to the slight reaction of the methoxide ion with the dimethylformamide. Traces of acidic impurities in the dimethylformamide caused salicylic acid to behave as a weak acid while in very pure dimethylformamide it acted as a medium strong acid.