Reactions of Halo Compounds

The photobehaviour of methyl iodide clusters is dependent on the mode of excitation. Thus, in a supersonic jet iodine molecules are formed, while a visible laser forms ions. Pulsed photolysis has been used to generate iodine atoms from trifluoromethyl iodide. 

The allyl- /2 radical is formed on irradiation of allyl-rf2 iodide at 193 nm. Allyl radicals are also formed by irradiation of allyl alcohol at the same wavelength. The dissociation in this instance occurs to form a triplet state following 7171 excitation. 

The results obtained from the irradiation at 235 nm of vibrationally excited dichloromethane suggest that there is higher non-adiabaticity for vibrationally excited molecules.Laser irradiation at 355 nm of methylene chloride and methylene bromide brings about ionization.A simple C-Br bond fission is the key step in the photodissociation of methylene dibromide at 248 nm. Ionization of methylene bromide in the 10-24 eV range has been reported. Irradiation of methylene iodide in water has provided evidence for the formation of iodine atoms and protons.Further work on the photochemical behaviour of methylene iodide has reported that vibrationally relaxed CH2l- T reacts with cyclohexene to afford norcarane.  

The photodissociation of bromoform at 193 nm has been studied using dispersed fluorescence.Bromoform also undergoes fission on irradiation at 234 and 267 nm. A series of 7z-alkylbromides has also been studied on irradiation at the same wavelengths. Prompt C-Br bond fission occurs on irradiation of bromoform at 248 nm. The isomerization of bromoform into isobromoform occurs on irradiation in water. Insertion of OH into isobromoform results in the formation of the final products, HBr, CO and formic acid.  

Bromine atoms are formed on irradiation of difluorobromochloro-methane at 267 nm. Photodissociation of trifluoroiodomethane at 248 nm has been studied using a high-resolution photofragment translational 

1 Reactions of Halo Compounds. - Calculations have been carried out to investigate the decomposition paths for methyl fluoride and methyl chloride. Methyl chloride undergoes photodissociation on irradiation at 157.6 nm. Photodissociation of methyl iodide at 266 nm has been studied. The methyl radical recombination has been followed by time-resolved photothermal spectroscopy. Methyl iodide also undergoes photochemical decomposition on a GaAs(llO) surface. Photolysis of methyl iodide at 236 nm in the gas phase brings about liberation of iodine atoms with a quantum yield of 0.69.  

Multiphoton dissociation of trifluoromethane has been studied. The results indicate that the product (C2F4) is enriched in C. The photodissociation 

Formation of iodine is detected tens of picoseconds after the irradiation of CH2ICH2I or CF2ICF2I in acetonitrile solution. In a continuation of their work on 1,1-dihalo compounds, Phillips and his group have investigated the photochemical behaviour of 1,1-dibromoacetic acid. Irradiation provides evidence for the formation of the iso-dibromoacetic acid (120). This is akin to the observations with 1,1-diodomethane. The authors propose that this species (120) could exhibit carbenoid character. Laser flash photolysis of 1,2-dibro-moethane at 248 nm in water provides a source of bromine atoms.  

A study of the elimination of Cl from 2-chlorobutane on irradiation at 193 nm has been reported. The photodissociation of jet-cooled CH3CF2CI at 235 nm has been studied, as has the photodissociation of iodobutane. This latter work used vacuum-UV mass-analysed threshold ionization. Media of different polarity and viscosity have been used in a study of the photochemical behaviour of 

2-iodooctane. The molecule absorbs at 270 nm where the transition is of no type. Homolytic reactions dominate but the radicals formed do not dimerize. Irradiation in a matrix of the long-lived radical [(CF3)2CF]2(C )C2F5 results in its decomposition, with the formation of the CF3 radical and the alkene (121).  

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Halide transfer reactions to metal cations are also very common processes. The reactions of halo compounds with metal cations are discussed in Section II.A.3.b. 

Participation of fluorocarbocations, derived from carboxylic acids and from halo acetones, in reactions of carbonyl compounds with sulfur tetrafluoride has been directly evidenced by trapping them with aromatic hydrocarbons [207, 20S],... 

Reaction of halo sulfonic acid esters with boranes 10-125 Alcoholysis of sulfonic acid derivatives 13-15 Vicarious substitution of aryl nitro compounds... 

The method described here belongs to a group of recently developed procedures comprising the spontaneous intramolecular acylation of active derivatives of metalated p-hydroxy alkanoates. These compounds are available by reactions of carbonyl compounds with ester enolates prepared from S-phenyl alkanethioates6 or phenyl alkanoates,15 as well as by Reformatsky16 or Darzens17 reactions of carbonyl compounds with phenyl a-halo alkanoates. 

The CIDNP experiments have been carried out to demonstrate an intervention of triplet radical pairs in many hydrogen abstraction reactions involving triplet car-benes. The following examples in reactions with halo compounds and ethers are of particular interest. 

Reaction of halo ketones or diazo ketones with boranes 0-102 Carbonylation of alkyl halides 0-104 Reaction between acyl halides and organometallic compounds 0-105 Reaction between other acid derivatives and organometallic compounds... 

One major reaction of aromatic compounds is electrophilic substitution and it was therefore natural to submit the present systems to electrophiles. Thus l,2-dihydro-2-methylbenz[e][l,2]azaborine (113 R = Me) is brominated and chlorinated in its 3-position to give compounds (186), of which (186 X = C1) was prepared authentically for identification, starting from w-chloro-2-aminostyrene. The main reaction was, however, deboronation to w-halo-2-aminostyrenes. 

The reaction has found little application so far however, one of the first examples of an asymmetric synthesis using peroxidases was the highly regio- and diastereo-selective halohydration of glycals to 2-deoxy-2-halo sugars in the presence of CPO [263]. Some examples of selective halogenation reactions of aromatic compounds using CPO optimized by directed evolution approaches are also known [264]. 

CONTENTS Preface, Brian Halton. Cydopropene-Vinylcar-bene Isomerization and Some Applications in Synthesis, John Warkentin and John McK. R. Wollard. Preparation and Subsequent Reaction Reactions of Halo- and Alkoxyhalocyclopro-panes, Leiv K. Sydnes and Einar Bakstad. The Phenylenes Synthesis, Properties and Reactivity, K.PeterC. Vollhardtand Debra L. Mohler. Cyclobutadienes and Azacyclobutadienes in the Synthesis of Valence Isomers of Six-Membered Aromatic and Heteroaromatic Compounds, Manfred Regitz, Heinrich ... 

Simons process — Electrochemical polyfluorination reactions of organic compounds are the only efficient way to industrial production of perfluorinated compounds. The reaction proceeds in the solution of KF in liquid HF (b.p. 19.5 °C), where the starting substances as alcohols, amines, ethers, esters, aliphatic hydrocarbons and halo-hydrocarbons, aromatic and heterocyclic compounds, sulfo- or carboxylic acids are dissolved. During anodic oxidation, splitting of the C-H bonds and saturation of the C=C bonds occur and fluorine atoms are introduced. 

Lithio compounds can also be obtained by exchange reactions with halo compounds, for example, the sodium salt of S-bromoindole can be converted to the S-lithio derivative by treatment with /-butyllithium, and this in turn allows synthesis of various S-substituted indoles. 

The reaction of -halo carbonyl compounds with primary amides is appropriate for oxazoles containing one or more aryl groups . Ureas form 2-aminooxazoles. Formamide can be used resulting in a free 2-position in the oxazole. A convenient synthesis of 5-substituted-4-cyanooxazoles 223 is based on the condensation of -hydroxy—cyanoenamines 222 with trimethyl orthoformate (Scheme 109). The cyanoenamine intermediates 222 are derived from Lewis acid-catalyzed Passerini reactions between /-butyl isonitrile and aldehydes <2002S1969>. 

The formation of norcaradiene derivatives with naphthalene [reaction (22)] lends some support to this scheme. This mechanism resembles a bimolecular two-step process suggested for the reaction of chloromethyl-aluminum compounds with olefins (199-201). On the other hand, a bimolecular one-step methylene transfer mechanism is generally accepted for the formation of cyclopropane derivatives by the reaction of halo-methylzinc compounds with olefins. This difference between the mechanism proposed for the cyclopropane formation from olefin and that for the ring expansion of aromatic compound may be ascribable to the difference in the stability of intermediates the benzenium ion (XXII) may be more stable than an alkylcarbonium ion (369). 

A number of related reactions, which occur by different mechanisms, have been reported. The intramolecular reaction of halo-malonates under carbon monoxide gives cyclic ketones (Eq. 5) [31,32]. This proceeds by mechanism C. Halo-malonates also couple with unsaturated compounds such as 1,3-dienes... 

The reaction of carbonyl compounds with glycerin-a-monochlorohydrin, CHjOHCHOHCHjCl, leads to cyclic halo acetals. Treatment of a,/3-olefinic aldehydes with alcohols saturated with dry hydrogen chloride causes the addition of the halogen acid to the double bond as well as acetalization to give /3-halo acetals. ... 

Certain nuclear substituents ortho to a newly formed diazonium group may interact to form a cyclic structure with or without retention of the nitrogen atoms. Such is the case in the diazotization of o-phenylene-diamine in aqueous solution, the product being 1,2,3-benzotriazole (81%). If the ortho substituent is an activated methyl group, an indazole is formed. Hydroxyl groups ortho or para to the diazonium group may interact to form internal condensation products called diazo oxides. These compounds may also form in the reaction of halo- and nitro-substituted aminophenols. 

D. A. Whiting, in Comprehensive Organic Chemistry. The Synthesis and Reactions of Organic Compounds. Vol. 1. Stereochemistry, Hydrocarbons, Halo Compounds, Oxygen Compounds (Ed. J. F. Stoddart), Chap. 4.2, Pergamon Press, Oxford, 1979. 

The use of organic halogen compounds as the starting products for the synthesis of other organic chemicals is too immense a field to do more than indicate some of the commercial applications. In his book I4S) on the chemistry of petroleum derivatives, Ellis includes a chapter on the production of alcohols and esters from alkyl halides, and also one on miscellaneous reactions of halo-paraffins and cycloparaffins. The manufacture of amyl alcohols and related products from the chlorides has been well covered 14 ) 1 )-A two-step process for the synthesis of cyclopropane by chlorinating propane from natural gas and dechlorinating with zinc dust was devised in 1936 152). A critical review of syntheses from l,3-dichloro-2-butene was published in Russia in 1950 (1-54). The products obtainable from the allylic chlorides are covered in a number of articles 14If 14 157). 

Pudovik, A.N., Nikitina. V.L, and Kurguzova, A.M., Reactions of organophosphorus compounds containing active methylene groups with methyl (l-chlorovinyl ketone and a-halo ethers, Zh. Obshch. Khim., 40, 291, 1970 J. Gen. Chem. USSR (Engl. Transl.), 40, 261, 1970. 

Rearrangement often occurs when attempts are made to replace a halogen atom by a different group. This applies particularly to reactions of halo carbonyl compounds, which will be illustrated by a few examples in which the carbon skeleton remains unchanged. 

Thus considerable care is needed when attempting to deduce the structure from reactions of halo carbonyl compounds. 

This reaction has been modified by temporarily terminating the reaction to obtain the dihydrofuran derivatives. In addition, this reaction has been carried out under an acidic conditions, such as in the presence of TFA, and by using 10% EtsN as the base. Moreover, o, j0-dichloroethyl ether has been used to substitute for the a-halo ketones. Other modifications include the reaction of dicarbonyl compounds with acetylenes and aldehydes. Furthermore, a general preparation of five-membered heterocycles, including furans—although not related to the Feist-Benary reaction—is also considered as a relevant modification. ... 

Then in 1965, we initiated studies on the reactions of halo-carbonyl compounds with tinfoil in the presence of the catalysts we had used in the former reactions (Eq. (2.1)) [5-23]. 

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