Sulfur stabilising anion

Related to these diphosphine dichalcogenides are the triphosphine trisulfides [R2P(S)]3CH (12) which can be prepared from lithiated methylene diphosphine disulfides upon treatment with thiophosphinic chlorides (Equation 9). Deprotonation of 12 with tBuLi gives a resonance-stabilised anion 13 containing a planar central carbanion whose charge is delocalised onto the three neighbouring phosphorus and sulfur atoms.32... 

The anomalous results with the sulfur-containing anions can also be explained. The stabilisation of an anion adjacent to sulfur is by overlap with the neighbouring SC bond (Section 2.2.3.2) and not by overlap with the lone pairs. If this is operating in the dithian-stabilised anion 4.56, it is no longer an X-substituent, but a Z-substituent, since the S—C bond is polarised away from the sulfur. Allyl anions with a Z-substituent are... 

Solvation of thiolates is similarly low in both protic and dipolar aprotic solvents because of the size and polarisability of the large weakly basic sulfur atom, so is unlikely to contribute appreciably to the observed solvent effect. The intermediate nitro radical anion is stabilised by H-bonding in a manner which retards its dissociation in the SrnI mechanism (upper equation in Scheme 10.35). In contrast, the electron flow in the direct substitution at X (lower equation in Scheme 10.35) is such that solvation by methanol promotes the departure of the nucleofuge. In summary, protic solvation lowers the rate of the radical/radical anion reactions, but increases the rate of the polar abstraction yielding disulfide. 

Lopez Garcia et al. [2] have described a rapid and sensitive spectrophotometric method for the determination of boron complex anions in plant extracts and waters which is based on the formation of a blue complex at pH 1 - 2 between the anionic complex of boric acid with 2,6-dihydroxybenzoic acid and crystal violet. The colour is stabilised with polyvinyl alcohol. At 600 nm the calibration graph is linear in the range 0.3-4.5 xg boron per 25 ml of final solution, with a relative standard deviation of 2.6% for xg/l of boron. In this procedure to determine borate in plant tissues, the dried tissue is treated with calcium hydroxide, then ashed at 400 °C. The ash is digested with 1N sulfuric acid and heated to 80 °C, neutralized with cadmium hydroxide and then treated with acidic 2,6-dihydroxybenzoic acid and crystal violet, and the colour evaluated spectrophotometrically at 600 nm. Most of the ions present in natural waters or plant extracts do not interfere in the determination of boron complex anions by this procedure. Recoveries of boron from water samples and plant extracts were in the range of 97 -102%. 

Trithiocarbonate S-oxides are reactive towards alkyllithiums [111] thio-philic additions were carried out at -78 °C. The resulting carbanions, stabilised by three sulfur groups, were quenched by water or by other electrophiles to afford trithioorthoester oxides. With enones, 1,4-addition was observed elimination of an alkanesulfenic acid led to /1-oxoketenedithioace-tals which could be transformed into 4-oxoalkanethioates. This Umpolung route allows the formal use of an (alkylthio)carbonyl anion. 

Dithians (thioketals) (48) are easily prepared by reaction of an aldehyde with propane-1,3-dithiol the dithians readily form 2-carbanions owing to the stabilising effect of the two adjacent sulfur atoms on the anion. The carbanion can subsequently be alkylated by treatment with primary or secondary alkyl halides,... 

Fig. 2.9 The stabilisation of an anion by adjacent sulfur, phosphoms and silicon groups...

Anionic surfactants, based on alkyl sulfates, are widely used as the basis for synthetic detergents, emulsifiers, stabilisers, and so on. Alkyl sulfates R0S03Me (where Me is Na, K and so on) under the conditions of commercial production, in particular, during the synthesis of detergents, can be produced by the interaction of the a-olefins of the unsaturated hydrocarbon fractions Cg-Cjg (olefin content no less that 97 wt%) and 98% sulfuric acid at the ratio of a-olefin/H2S04 = 1/1.2-1.4 mole, with further neutralisation of the imreacted H2SO4 and saponification of the synthesised alkyl sulfur acid ... 

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