Effect of base on alkyltriphenylphosphonium salts in polar aprotic solvents

When arylmethyl phosphonium salts are treated with a base (e.g., t-BuOK or NaH) they homocouple to form symmetric 1,2-diarylethenes. In some cases, dilution and (or) use of excess base lead to very high yields of the product. This reaction is solvent sensitive: the reaction occurs only when polar aprotic solvents such as acetonitrile or DMSO are used. Other alkyl phosphonium salts (e.g., ethoxycarbonylmethyltriphenylphosphonium bromide and n-butyltriphenylphosphonium bromide) form a ylid (when an α-carbonyl group is present) or lose a phenyl group to form alkyldiphenylphosphine oxides when treated with the base. Mechanistic investigation of the homocoupling reaction indicates that the reaction proceeds through a ylid that acts as a nucleophile on an unreacted phosphonium salt. The resulting adduct undergoes elimination to form the observed product. The E/Z ratio seems to depend on the amount of the base used and the phosphonium salt involved.Key words: phosphonium salts, homocoupling, 1,2-diarylalkene, Ylids.

A Novel Chromogenic Ester Agar Medium for Detection of Salmonellae

ABSTRACT A novel agar medium, chromogenic Salmonella esterase (CSE) agar, for the differentiation of salmonellae is described. The agar contains peptones and nutrient extracts together with the following (grams per liter unless otherwise specified): 4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)-vinyl]-quinolinium-1-(propan-3-yl carboxylic acid) bromide (SLPA-octanoate; bromide form), 0.3223; lactose, 14.65; trisodium citrate dihydrate, 0.5; Tween 20, 3.0; ethyl 4-dimethylaminobenzoate, 0.035% (wt/vol), novobiocin, 70 mg liter−1. The key component of the medium is SLPA-octanoate, a newly synthesized ester formed from a C8fatty acid and a phenolic chromophore. In CSE agar, the ester is hydrolyzed by Salmonella spp. to yield a brightly colored phenol which remains tightly bound within colonies. After 24 h of incubation at 37 or 42°C, colonies of typical Salmonellaspp. were burgundy colored on a transparent yellow background, whereas non-Salmonella spp. were white, cream, yellow or transparent. CSE agar was evaluated by using a panel of strains including a high proportion of Salmonella and non-Salmonella strains giving atypical reactions on other differential agars. The sensitivity (93.1%) of CSE agar for non-typhi salmonellae compared favorably with those of Rambach (82.8%), xylose-lysine-deoxycholate (XLD; 91.4%), Hektoen-enteric (89.7%), and SM ID (91.4%) agars. The specificity (93.9%) was also comparable to those of other Salmonellamedia (SM ID agar, 95.9%; Rambach agar, 91.8%; XLD agar, 91.8%; Hektoen-enteric agar, 87.8%). Strains of Citrobacter freundii and Proteus spp. giving false-positive reactions with other media gave a negative color reaction on CSE agar. CSE agar enabled the detection of >30 Salmonellaserotypes, including agona, anatum,enteritidis, hadar, heidelberg,infantis, montevideo, thompson,typhimurium, and virchow, which accounted for 91.8% of the salmonella isolates recorded by the Public Health Laboratory Service (Colindale, London, England) for 1997.