Replacement of hydrogen by sulfur groups

Addition of sulfinic acids to aldehydes affords -hydroxy sulfones  

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Replacement of hydrogen by the nitro group is one of the most important reactions in the whole of organic chemistry, particularly in the aromatic series. It is effected not merely by nitric acid itself in various concentrations or in mixtures or solvents, but also by a number of other reagents which, however, are less important than nitric acid the commonest reagent is the mixture of nitric and sulfuric acid known as nitrating acid. 

Sulfur or the thiol group may be substituted for functional groups as well as for hydrogen in the presence of nickel sulfide catalysts. Simultaneous replacement of oxygen by sulfur in carbonyl compounds and hydrogenation to thiols may be carried put over nickel sulfide catalysts. 

The replacement of oxygen by sulfur results in a red shift of the first absorption band of around 0.21 eV. However, the substitution of the terminal hydrogen for the methyl group does not modify the band position, fir the four derivatives there is a flux of charge from the phenolic part toward the rest of the molecule. This flux is larger in pCA and pCMe, 0.22 e, than in pCTA and pCTMe , 0.13 e. Consequently, the delocalization of the charge is larger in the excited state of the 0X0 derivatives that becomes more stable than the thio derivatives. 

Introduction of the sulfonic acid group by replacement of hydrogen is much less important in the aliphatic than in the aromatic series. On direct sulfonation of alkanes by sulfuric acid, oleum, or sulfur trioxide side reactions (isomerization, dehydrogenation, oxidation, and formation of sulfone bonds) occur to such an extent that this process has found hardly any practical applications. 

We continue to be intrigued by spectroscopically observable intermediates that have thusfar eluded isolation and complete characterization. To this end, ongoing research is based on a derivative of bme-daco which has replaced hydrogens by methyl groups on the carbons alpha to sulfur, Sterically encumbered sulfur sites are expected to enhance the possibility of isolating partially oxidized products. 

Replacement of a hydrogen of benzene by chlorine is termed chlorination. When one or more hydrogens are replaced by an -NO2 (nitro group), it is called nitration. Reaction of benzene with sulfuric acid, a reaction known as sulfonation, leads to a sulfonic acid. Note that in each substitution reaction, a small hydrogen-containing compound is formed. 

Up to three of the hydrogens on a benzene ring can be replaced with a nitro (-NO2) group by reaction of nitric acid in sulfuric acid. When two hydrogens are replaced by nitro in this manner (dinitration), one isomer, the meta- or 1,3-, predominates. When three hydrogens are replaced (trinitration), the predominant isomer is the 1,3,5-isomer mera-dinitrobenzene is made by this method as a starting material for mera-phenylenediamine, one of the components in the manufacture of a heat-resistant nylon sold in the U.S. as Nomex by DuPont. 

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