P chlorination

Nitrogen mustards such as 23 decompose to yield aziridinium ions 24 (Scheme 8.14). " As in the case of sulfur mustards, the reaction involves rate-limiting intramolecular displacement of p-chlorine by nitrogen. The resulting aziridinium ions... 

More Heavily Fluorinated Compounds. The series of fluo-rinated ethanes in Scheme 3.18 indicates that the fluorine nucleus of a CH2F group is increasingly shielded as the number of P-fluorines increases, unlike the situation observed for an increasing number of P-chlorine substituents (Scheme 3.12). Note that as one accumulates fluorines at the P-position, the three-bond H—F coupling constant becomes progressively smaller. 

Few monofluoro vinyl ethers have been reported in the literature. The NMR data for one example is given. It can be seen that the P-ether substituent shields the fluorine much more than does a P-chlorine substituent. 

Denis and coworkers [37] could trap transient simple phosphaalkene 33, generated by HC1 elimination from chlorophosphine 32 at low temperatures [38], by ethyl diazoacetate at -50°C. Aromatization of the initially formed isomeric E-/Z-cycloadducts 35 to [l,2,4]diazaphospholes 36 could be achieved via P-chlorination/ dehydrochlorination sequence at -30°C using /V-chIorosuccinimidc (Scheme 10). 

The main products under all variations of R and R are the P2-chlorinated triphosphanes. Side reactions such as SiMe3/Cl exchange, P—P cleavage by LiP(SiMe3)R, or transmetallations take place only to a small extent. MeP(SiMe3)2 is an exception inasmuch as it reacts with P-chlorinated phosphanes to yield tri- and even tetraphosphanes. 

Sclumninger, P, Chlorine Principle > and fnduxtriul Practice, John Wiley Sons. Inc.. New York, NY. 2000. 

An unprecedented one-pot stereoselective synthesis of 2-azetidinone P-chlorinated allylic alcohols 23, which can also be considered as functionalized allylsilanes, has been developed, by tin(IV) chloride-mediated reaction of propargyltrimethylsilane and 4-oxoazetidine-2-carbaldehydes <02CEJ1719>. An explanation for the formation of P-chlorovinyl alcohols involves a stepwise process with the chlorination proceeding via a silicon stabilized carbocation. 

Lung irritants (iungeweiunde Kamp/atoJfeK c.p.. chlorine, phosgene, diphoKgeitc. rhiorpicriii, lewisite B. 

Mephenesin is weakly active and short-lived because of facile metabolism of the primary hydroxyl group. Carbamy-lation of this group increases activity. p-Chlorination increases the lipid/water partition coefficient and seals off the para position from hydroxylation. 

Vainio H, Hesso A, Jappinen P. Chlorinated dioxins and dibenzofurans in the environment a hazard to public health Scand J Work Environ Health 1989 15(6) 377-82. 

The homogeneity of the material for its matrix composition was verified for the elements Cl, S, Ca, K and P. Chlorine was determined after an oxygen flask combustion by an argentometric titration with potentiometric detection sulphur was determined... 

The starting material 3-chloro-5,5-dimethylcyclohex-2-en-1-one (1) is easily synthesized from dimedone by the general methodology developed by Clark and Heathcock.3 The p-chlorine can also be replaced with a variety of carbon- and heteronucleophiles, and p-chloroenones can be easily reduced by zinc/silver couple to the corresponding enone. h... 

Further papers of general synthetic interest include the full paper on the U02Cl2-Me0H-catalysed photoreactions of enones (Vol. 7, p. chlorination... 

Such eliminations occur easily because in the process steric strain is relieved. It should be pointed out that, in spite of being significantly inhibited because of steric repulsions between the o- and the a- and P-chlorines (Section 10 p. 411), conjugation between the benzene and the ethylene tt-electron systems of the resulting ethylenes presumably affords an additional driving force for dechlorination. 

The esr spectrum of the reactive radical (C6Cl5)2CH- (p. 360) is shown in Fig. 41 (Barrios, 1989). Beside the splitting into two groups of lines due to the a-proton, it is remarkable that those caused by the o- and the p-chlorines are resolved. The 19 lines observed indicate that the hcc values are practically identical for o- and / -Cl. This exceptional resolution is traced to the absence of strongly coupling with a- C1 and Cl. 

Possible additional support for a photonucleophilic hydride transfer mechanism comes from further observations on the photolysis of PCP. When this compound was irradiated in methanol rather than in water, no oxidation or displacement of chlorine by hydroxyl was detected instead, photoreduction produced primarily 2,3,5,6-tetrachlorophenol (XVI) together with a small proportion of what seemed to be the 2,3,4,5-tetra-chloro isomer (Figure 6) (52). Hydrogen abstraction from solvent by polychlorophenyl radicals is expected to produce some of each of the three isomers representing replacement of an o-, m-, and p-chlorine, with the first two predominating because of doubled probability. 

As in case of furan derivatives, the methods for the synthesis of bis(polyfluoroaIkyl thiophenes are more studied. Huorination of 2,5-thiophendicarboxylic acid with sulfur tetrafluoride leads to the formation of 2,5-bis(trifluoromethyl)thiophen." Fluorination of perchlorinated thiophen 154 with AgF gives thiophene 155 and replacement of the p-chlorine atoms by fluorine could not be achieved in this reaction. 

Figure 7.2. Effects of different bleaching sequences on the fibre surface content of lignin TCF, total chlorine free ECF, elemental chlorine free. The bleaching steps are oxygen delignification (O), ozone (Z), peroxide (P), chlorine dioxide (D) and alkali extraction (E). (From ref. (4) with permission)...

Medvedeva et al. first investigated the substituted propynals 303 as aldehyde substrates involved MBH reactions. The initial attempt to conduct the MBH reaction in the presence of TiCU was unsuccessful because of oligomerization of the reaction mixture. However, promotion with TiCU and a catalytic amount of dimethyl sulfide in the chalcogeno-MBH reaction led to 2-[(Z, )-chloromethylidene]-3-hydroxy-1 -phenyl-5-organylpent-4-yn-1 -ones 304 by tandem a-hydroxyethynylation/p-chlorination of l-phenylprop-2-yn-l-one (Scheme 2.166). ... 

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