PTC method

Gutfelt et al. (1997) have evaluated various ME formulations as reaction media for synthesis of decyl sulphonate from decylbromide and sodium sulphite. The reaction rate was fast both in water-in-oil and in bicontinuous ME based on non-ionic surfactants. A comparison was made with this reaction being conducted in a two-phase. system with quats as phase-transfer catalyst but was found to be much less efficient. However, when two other nucleophiles, NaCN and NaNOj, were used the PTC method was almost as efficient as the ME media. It seems that in the case of decyl sulphonate there is a strong ion pair formation between the product and the PTC. The rate in the ME media could be further increased by addition of a small amount of a cationic surfactant. 

Poly ethers were next synthesized from isosorbide by means of a MW-assisted PTC method (Eq. 10). In addition to increasing the rate of the reaction, the MW affected the structure of the polymer (determined by MALDI/TOF mass spectrometry Tab. 5.7). Polymers of higher molecular weights, with ethylenic groups as chain terminations, were obtained conventional heating led to shorter hydroxylated compounds [21]. 

It is clear therefore that this preparative procedure may only be of value for the formation of a restricted range of alkene target molecules. Recent procedures include the use of the non-nucleophilic base, l,8-diazabicyclo[5.4,0]undec-7-ene (DBU),18 and the use of PTC methods.19 One useful example is provided by the ready conversion of 3-bromocyclohexene (Expt 5.68) into cyclohexa-1,3-diene (Expt 5.13) where the base employed is quinoline. 

PTC methods for the oxidation of water-insoluble acid-sensitive alcohols have been described which use an aqueous sulphuric acid solution of potassium dichromate, dichloromethane and catalytic amounts of tetrabutylammonium hydrogen sulphate.103... 

Three PTC methods are worthy of note. In the first the alkyl halide is treated with sodium cyanide in decane solution in the presence of catalytic amounts of hexadecyltributylphosphonium bromide.1673 In the second tetraethylammo-nium cyanide in molar quantities is used in dichloromethane solution with the alkyl halide.1676 In the third method, which is reported to be most satisfactory in the case of allylic and benzylic halides, a solid/liquid system of potassium cyanide and 18-crown-6 ether is employed.168... 

The chloramine derivatives (ArS02NClNa) of a variety of other aryl-sulfonamides (Ar = phenyl, o-tolyl, p-chlorophenyl,/>-nitrophenyl, and o-carboalkoxyphenyl) have been used successfully in these catalytic oxy-aminations. Since only chloramine-T (Ar = p-tolyl) and chloramine-B (Ar = phenyl) are commercially available, we have developed a convenient procedure for generating the chloramines in situ for use in the modification involving phase-transfer catalysis. One simply stirs a suspension of the arylsulfonamide with an equivalent of sodium hypochlorite (Clorox) until a homogeneous solution is obtained. When this solution is used in the PTC method (see Ref. 2 for experimental details), the yields of oxyaminated product are comparable with those obtained with isolated chloramine salts. 

The PTC method gives poor results with trisubstituted and 1,1-disub-stituted olefins. The oxyamination product may still form, but it is accompanied by a number of by-products. Fortunately, this class of olefins is successfully oxyaminated by the alternative procedure (B). Methyl-cyclohexene, a-methylstyrene, 2-methyl-2-hepten-6-one, and its ketal are examples of olqfins that give oxyamination products in good yield following procedure B. 

Since dibromocarbene is more susceptible to hydrolysis than dichlorocarbene, dibro-mocarbene addition by the PTC method often gives the expected adducts in lower yields than those of the dichlorocarbene addition. Use of excess tribromomethane , execution of the reaction at ambient or lower temperature and addition of a small amount of alcohol have been recommended to improve the yields. Diiodocarbene has also been generated by PTC procedures and has been added to alkenes . However, the CHl3/r-BuOK method appears to be superior . It has also been pointed out that the Cl2 adducts are sometimes rather unstable when they are prepared by the PTC method, probably due to contamination of some sensitive byproducts . 

Method A CHCI3, aq NaOH, PTC Method B CHCI3, r-BuOK. Reaction was additionally sonicated. 

Method A CHClj, base, PTC Method B CCljCO Na, A Method C CCljCOjEt, NaOMe Method D PhHgCBrClj, A Method E CljSiCClj, A or TMSCClj, F. ... 

Method A CHCI3, base, PTC Method B CCljCOjEt, NaOMe Method C PhHgCBrClj, 80°C. 

Method A CHClj, base, PTC Method B PhHgCBrClj, A. Additionally l,l-dichloro-2-(dich-loromethoxymethyl)-2-methylcyclopropane was formed (20%), the mixture was separated by GC. The mixture was separated by GC, the isomer with shorter retention time mp 39 -40 C. Isomer ratio 48 52. Isomer ratio 1 1. Additionally l,l-dichloro-2-(2-dichloromethoxyethyl)-2-methylcydo-... 

Method A CHBTj, base, PTC Method B CHBrj, t-BuOK Method C PhHgCBrj, A. 

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