Dehydrohalogenation chloride

In early work, vinyl chloride had been heated with stoichiometric amounts of alkaU alkoxides in excess alcohol as solvent, giving vinyl ethers as products (210). Supposedly this involved a Williamson ether synthesis, where alkaU alkoxide and organic haUde gave an ether and alkaU haUde. However, it was observed that small amounts of acetylene were formed by dehydrohalogenation of vinyl chloride, and that this acetylene was consumed as the reaction proceeded. Hence acetylene was substituted for vinyl chloride and only catalytic amounts of alkaU were used. Vinylation proceeded readily with high yields (211). 

Phosgene reacts with a multitude of nitrogen, oxygen, sulfur, and carbon centers. Reaction with primary alkyl and aryl amines yield carbamoyl chlorides which are readily dehydrohalogenated to isocyanates. Secondary amines also form carbamoyl chlorides. 

The monomer 4-styrenesulfonic acid was prepared by dehydrohalogenation of -bromoethjibenzene—sulfonyl chloride. The potassium salt can be polymerized in aqueous solution (222). The sulfonation of cross-linked polystyrene beads is being carried out in industry with concentrated sulfuric acid. 

Addition to the Double Bond. Chlorine, bromine, and iodine react with aHyl chloride at temperatures below the inception of the substitution reaction to produce the 1,2,3-trihaLides. High temperature halogenation by a free-radical mechanism leads to unsaturated dihalides CH2=CHCHC1X. Hypochlorous and hypobromous acids add to form glycerol dihalohydrins, principally the 2,3-dihalo isomer. Dehydrohalogenation with alkah to epicbl orobydrin [106-89-8] is ofgreat industrial importance. 

Halobutyl Cures. Halogenated butyls cure faster in sulfur-accelerator systems than butyl bromobutyl is generally faster than chlorobutyl. Zinc oxide-based cure systems result in C—C bonds formed by alkylation through dehydrohalogenation of the halobutyl to form a zinc chloride catalyst (94,95). Cure rate is increased by stearic acid, but there is a competitive reaction of substitution at the halogen site. Because of this, stearic acid can reduce the overall state of cure (number of cross-links). Water is a strong retarder because it forms complexes with the reactive intermediates. Amine cure may be represented as follows ... 

The epoxidation is generally conducted in two steps (/) the polyol is added to epichlorohydrin in the presence of a Lewis acid catalyst (stannic chloride, boron triduoride) to produce the chlorohydrin intermediate, and (2) the intermediate is dehydrohalogenated with sodium hydroxide to yield the aliphatic glycidyl ether. A prominent side-reaction is the conversion of aliphatic hydroxyl groups (formed by the initial reaction) into chloromethyl groups by epichlorohydrin. The aliphatic glycidyl ether resins are used as flexibilizers for aromatic resins and as reactive diluents to reduce viscosities in resin systems. 

The first /3 -lactam was produced by addition of a ketene to an imine and there are now many examples of this type of approach. The ketenes are most frequently generated in situ from acid chlorides by dehydrohalogenation, but have also been produced from diazo ketones, by heating of alkoxyacetylenes and in the case of certain cyanoketenes by thermolysis of the cyclic precursors (162) and (163). 

Cyclohexyl bromide, for exfflnple, is converted to cyclohexene by sodium ethoxide in ethanol over 60 times faster than cyclohexyl chloride. Iodide is the best leaving group in a dehydrohalogenation reaction, fluoride the poorest. Fluoride is such a poor leaving group that alkyl fluorides are rarely used as starting materials in the preparation of alkenes. 

We have already encountered the ir, a, and p quantities. The 8h term is inserted to account for the cavity effect. Equation (8-80) is a 12-parameter equation for which considerable generality is claimed, in that it is said to be applicable to chemical rates and equilibria, spectra, solubilities, partition coefficients, and even biological responses. Usually, of course, by judicious selection of solvents, it is possible to reduce the number of parameters by ensuring that some terms are negligible.An example requiring most of the parameters in Eq. (8-80) is the solvolysis/dehydrohalogenation of r-butyl chloride in 21 HBD and non-HBD solvents, for which this correlation was found ... 

Triethylamine has been found to dehydrohalogenate acid chlorides having a-hydrogens to give ketenes according to the reaction. In an interesting variation on this... 

Dehydrohalogenation, of cyclohexanc-carbonyl chloride to dispiro-[S.1.5.1]tetradecane-7,14-dione,... 

Substituted dibenz[6,/]oxepin-10(l l//)-ones can be reduced with sodium borohydride or lithium aluminum hydride and treated with thionyl chloride to afford the chloro derivatives which undergo dehydrohalogenation when heated or treated with base to give products... 

A rather broadly applicable method leading to products which can be further modified starts from 3,8-diaryl-l,2-diazacycloocta-2,8-dienes 4.23,24 With /V-bromosuccinimide dihalogenation occurs which, after a double dehydrohalogenation, gives 3,8-diphenyl-1,2-di-azocine (5 Ar = Ph, X = H) in low yield. The reaction with sulfuryl chloride to give tetra-... 

Goering and coworkers201 studied the kinetics of base-promoted dehydrohalogenation of several series of cis- or frans-2-chlorocycloalkyl aryl sulfones. For the trans-2-chlorocyclohexyl series reacting with sodium hydroxide in 80% ethanol at 0 °C the p value was 1.42. The mechanism was considered to involve rate-determining carbanion formation, with the subsequent loss of chloride ion in a fast step. 

Carbodiimides have been prepared by desulfurization of thioureas by metal oxides, by sodium hypochlorite,4 or by ethyl chloroformate in the presence of a tertiary amine by halogena-tion of ureas or thioureas followed by dehydrohalogenation of the N,N -disubstituted carbamic chloride 8 and by dehydration of disubstituted ureas using -toluenesulfonyl chloride and pyridine.7 The method described above is a modification of that of Campbell and Verbanc. ... 

A one pot synthesis of isoxazolines 78a-f involves base mediated 1,4-addition of malonate or alcohol 76 possessing an allylic substituent, conversion of the resulting nitronate to the a-chloroaldoxime (hydroxymoyl chloride 77) and its subsequent dehydrohalogenation to the nitrile oxide intermediate which cyclizes to isoxazoline 78 (Eq. 7, Table 6) [32]. 

Two other results will now be pointed out which presumably also require reinterpretation in the light of the reaction behavior of iminooxophosphoranes. Thus the gas phase pyrolysis of diphenylphosphoryl azide is reported to give monomeric 92 50) and the dehydrohalogenation of phenylphosphoric adamantylamidic chloride with methylhydrazine the heterocumulene 93 51), which is even considered resistant to water. Since partly correct analytical values are available, 92 and 93 may well be oligomers. 

Dehydrohalogenation of the 314 proceeded in excellent yield under the action of morpholine or piperidine at rt, during double bond formation between the C-l and C-2 atoms <2003CHE640>. The active methylene group of 3,4-dihydro-1 ///>//-[ 1,4 oxazino[3,4- quinazolin-6-onc 315 readily condensed with aromatic aldehydes at 160 °C in a melt to give the 1-benzylidenes, and coupled with aryldiazonium chlorides to give the arylhydrazono derivatives <1996BMC547>. 

Alkylidene sulfenes (75), generally prepared by the dehydrohalogenation of alkylsulfonyl chlorides, add readily to electron-rich multiple bonds. For example, with enamines, the thietane dioxide (e.g., 76) is formed diazoalkanes yield thiirane dioxides (episulfones) and imines (Schiff bases) afford 1,2-thiazetidine 1,1-dioxides. There are available numerous reviews of sulfenes, including cycloaddition reactions.102... 

Sulfonyl imides (78) are, like sulfenes, prepared by dehydrohalogenation of the corresponding sulfonyl chlorides (79) (usually called sulfamoyl chlorides). Like sulfenes, they take part in [2 + 2] and [4 + 2] cycloaddition reactions with electron-rich alkenes or with 1,3-dienes, yielding 1,2-thia-zetidine 1,1-dioxides (80)104 or dihydro-1,2-thiazines (81),105 respectively. 

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