Dehydrochlorination, of acid chlorides

Dehydrobromination, of 2 bromo-dodecanoic acid, 37, 29 of 10,11-dibromohendecanoic acid with sodium amide, 32, 104 of 9,10-dibromooctadecanoic acid with sodium amide, 37, 77 Dehydrochlorination, of acid chlorides,... 

Dehydrochlorination of acid chlorides of type RCH2COCI by proton sponge 1 in order to produce monoketenes is not directly realized232,233, but proceeds in the presence of benzoylquinine (BQ) as a shuttle base . The in situ generated ketenes were used further for the synthesis of optically active /3-lactams 258 (Scheme 48). Additionally, a method providing fraws-isomers of 258 with the help of diamine 1 has recently been elaborated234. 

Leckta et al. recently described an efficient procedure for the in situ generation of reactive monosubstituted ketenes through dehydrochlorination of acid chlorides promoted by NaH/15C5 in THE. This new methodology was applied to a cost-effective, catalytic asymmetric synthesis of P-lactams and a-chloroesters, pharmaceutically useful classes of compounds (Eq. 18). 

The chemistry of nitrile oxides, in particular their application in organic synthesis, has been continuously developed over the past two decades and represents the main theme of this chapter. The parent compound, fulminic acid (formonitrile oxide), has been known for two centuries, and many derivatives of this dipole have been prepared since that time. Several simple and convenient methods for the preparation of nitrile oxides have evolved over the years. Dehydrochlorination of hydroximoyl chlorides was first introduced by Werner and Buss in 1894 (1). A convenient synthesis of isoxazoles was reported by Quilico et al. (2 ), and then the discovery of nitrile oxide cycloadditions to alkenes was subsequently noted by the same group (5). 

In the dehydrochlorination of acethydroxamoyl chloride, using aqueous sodium carbonate, interaction of the hydroxamic acid and the generated nitrile oxide with formation of the 1 1 adduct XXXIX was observed ( ). 

The initial examples of ketene preparation utihzed efimination reactions from carboxylic acid derivatives in the preparation of diphenylketene (1) by the dehalogenation of 2-chlorodiphenylacetyl chloride with zinc (Eqns (4.1)), and the dehydrochlorination of diphenylacetyl chloride... 

Ultimately, as the stabilization reactions continue, the metallic salts or soaps are depleted and the by-product metal chlorides result. These metal chlorides are potential Lewis acid catalysts and can greatiy accelerate the undesired dehydrochlorination of PVC. Both zinc chloride and cadmium chloride are particularly strong Lewis acids compared to the weakly acidic organotin chlorides and lead chlorides. This significant complication is effectively dealt with in commercial practice by the co-addition of alkaline-earth soaps or salts, such as calcium stearate or barium stearate, ie, by the use of mixed metal stabilizers. 

Dehydrochlorination of 1,1,2-trichloroethane [25323-89-1] produces vinyHdene chloride (1,1-dichloroethylene). Addition of hydrogen chloride to vinyHdene chloride in the presence of a Lewis acid, such as ferric chloride, generates 1,1,1-trichloroethane. Thermal chlorination of 1,2-dichloroethane is one route to commercial production of trichloroethylene and tetrachloroethylene. 

Dehydrochlorination of chlorinated derivatives such as 1,1,2-trichloroethane may be carried out with a variety of catalytic materials, including Lewis acids such as aluminum chloride. Refluxing 1,1,2-trichlorethane with aqueous calcium hydroxide or sodium hydroxide produces 1,1-dichloroethylene in good yields (22), although other bases such as magnesium hydroxide have been reported (23). Dehydrochlorination of the 1,1,1-trichloroethane isomer with catalytic amounts of a Lewis acid also yields 1,1-dichloroethylene. Other methods to dehydrochlorinate 1,1,1-trichloroethane include thermal dehydrochlorination (24) and by gas-phase reaction over an alumina catalyst or siUca catalyst (25). 

Jamieson and McNeill [142] studied the degradation of poIy(vinyI acetate) and poly(vinyI chloride) and compared it with the degradation of PVC/PVAc blend. For the unmixed situation, hydrogen chloride evolution from PVC started at a lower temperature and a faster rate than acetic acid from PVAc. For the blend, acetic acid production began concurrently with dehydrochlorination. But the dehydrochlorination rate maximum occurred earlier than in the previous case indicating that both polymers were destabilized. This is a direct proof of the intermolecular nature of the destabilizing effect of acetate groups on chlorine atoms in PVC. The effects observed by Jamieson and McNeill were explained in terms of acid catalysis. Hydrochloric acid produced in the PVC phase diffused into the PVAc phase to catalyze the loss of acetic acid and vice-versa. 

A PPV derivative which is twofold phenylsubstituted at the vinylene unit, poly(l,4-phenylene-l,2-diphenylvinylene DP-PPV), (71b) (see also the discussion of dehydrochlorination of unsymmetrically substituted para-xylylene dichlorides in Section 3.1) was first synthesized by Smets et al., using acid-catalyzed elimination of nitrogen from l,4-bis(diazobenzyl)benzene 83 [106]. The yellow products obtained are fully soluble in common organic solvents (toluene, chloroform, ethylene chloride, DMF, THF). 

Arylsydnone-4-carbonitrile oxides, which are generated in situ by thermal dehydrochlorination of the corresponding hydroximic acid chlorides, undergo 1,3-dipolar cycloadditions with sydnone-4-carbonitriles to give 3-aryl-4-[5-(3-arylsydnonyl)-l,2,4-oxadiazol-3- yl]sydnones 228 (392). 

The mechanism of the formation of compound 67 has been studied by Higa and Krubsack [41] in detail, as shown in Scheme 15. Namely, the initial step of the reaction of the cinnamic acid derivative 66 with thionyl chloride is an electrophilic addition of thionyl chloride across the double bond of cin-namoyl chloride to form the sulfinyl chloride intermediate (66a), which is then converted to 68 by the Pummerer reaction. Dehydrochlorination of 68... 

Endrin is a stereoisomer of dieldrin produced by the reaction of vinyl chloride and hexachloro-cyclopentadiene to yield a product which is then dehydrochlorinated and condensed with cyclopentadiene to produce isodrin. This intermediate is then epoxidized with peracetic or perbenzoic acid to yield endrin. An alternative production method involves condensation of hexachlorocyclopentadiene with acetylene to yield the intermediate for condensation with cyclopentadiene (EPA 1985e IARC 1974). 

Aroylbutyric acids react with oxalyl chloride to produce mixtures of open-chain isomers of the chlorides and unsaturated lactones, the latter being formed by dehydrochlorination of the cyclic isomers of the chlorides [86JCS(P2)355]. It was presumed in that paper that the two chloride isomers were formed from the initial acids in two independent competitive reaction pathways. 

The double dehydrochlorination of 2,6-dichloro-l-oxacyclohexanes to 4//-pyran (5) and its 4-methyl homolog7,9,19,57 has been mentioned in Section III,A. Another double dehydration occurs in the synthesis of 4,4-diphenyl-4//-pyran 280 in 80% yield by the action of tosyl chloride on 2,6-dihydroxytetrahydropyran 279 in pyridine.296 Another diphenyl derivative (mp 56°C) was reported to be isolable from a mixture after the reaction of cellulose with benzene in sulfuric acid.297... 

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