Olefins halides, from

A model consistent with the stereochemical outcome of the reaction and with the role of the halide has been proposed (Fig. 10). This model suggests side-on olefin binding and reorganization of the halide ligands. In such geometry, a steric interaction between the unbound olefin and apical halide may justify the dramatic increase in enantioselectivity observed upon changing the halide from cr to r. 

The latest addition to the theories of cationic polymerisation is the self-initiation theory of Kennedy [12]. According to this theory, initiation can take place in certain systems by a reaction between the metal halide and the olefin in which a hydride ion is abstracted by the metal halide from an allylic position in the monomer ... 

K. A. Cooper, E. D. Hughes, and C. K. Ingold, "The Mechanism of Elimination Reactions. Part III. Unimolecular Olefin Formation from Tert.-Butyl Halides in Acid and Alkaline Aqueous Solutions," JCS 140 (1937) 1280. 

L3 Elimination of Hydrogen Halide from Halo-olefinic Compounds... 

Recently, catalyst 50 (n > 4) was reported highly active and selective for olefin synthesis from alkyl halides with aqueous sodium or potassium hydroxide without the formation of by-product alcohols 172). The active catalyst structures were suggested to involve self-solvated polymeric alkoxides 173) 52 and/or complexed hydroxides 53. 

The absence so far of unequivocal proof of carbene formation by a-elimination of hydrogen halide from organic halides and related reactions using hydroxide and alkoxide ions or weaker bases suggests that more detailed investigations of some reported carbenoid reactions may be justified. Thus carbenoid behaviour in the reaction between benzal chloride and potassium t-butoxide in the presence of olefins seems to be critically dependent upon the nature of the solvent (McElvain and Weyna, 1959 Cawley and Westheimer, 1960) and the reaction temperature (Hodgkins et al., 1964). 

Hydrides from carboxylic acids Carboxylic acids from hydrides Carboxylic acids from hydrides Esters from hydrides Hydrides from aldehydes Hydrides from aldehydes Alkyls from aldehydes Ketones from methylenes Ketones from ketones Alkyls from olefins Acetylenes from halides also acetylenes from acetylenes Esters from alcohols also esters from carboxylic acids Alkyls from olefins Alkyls from olefins... 

The four-coordinate sqnare planar iron(n) porphyrins discussed above are not only of great valne in heme protein model chemistry, but also in chemical applications, since they undergo a wealth of ligand addition reactions. For example it has been shown that TPPFe complexes are active catalysts for important carbon transfer reactions in organic chemistry and are found to catalyze the stereoselective cyclopropanation of aUcenes, olefin formation from diazoalkanes, and the efficient and selective olefination of aldehydes and other carbonyl compounds. The active species in these carbon transfer reactions are presumably iron porphyrin carbene complexes. " It was also found that ferrous hemin anchored to Ti02 thin films reduce organic halides, which can pose serious health problems and are of considerable environmental concern because of their prevalence in groundwater. ... 

A triple bond may be formed by dehydrohalogenation of dihalides and olefinic halides of the general types RCX= CHj, RCH= =CHX, RCH= =CXR, RCHXCHjX, RCHXCHXR, RCHjCHX, and RCXjCHjR. The choice of a base depends somewhat on the position desired for the triple bond in the product. Sodium amide tends to rearrange the triple bond toward the end of the chain," and potassium hydroxide favors reverse isomerization toward the center of the chain,Although neither rearrangement is dependable from a synthetic standpoint, it is best to choose the base favoring the desired product. 

The condensation of saturated hydrocarbons with haloolefins in the presence of anhydrous aluminum chloride also results in the formation of alkyl halides, as in the preparation of l-chloro-3,4-dimethylpentane from isobutane and allyl chloride (40%). Under the same conditions, alkyl halides react with olefinic halides to give dihaloalkanes. unsym-Heptachloropropane is synthesized from tetrachloroethylene and chloroform (93%). ... 

Olefinic amino aciefe and alkoxy amino acids are obtained by this method from olefinic halides and halo ethers, respectively. 

The formation of olefinic nitriles from allylic halides is best accomplished with dry, powdered cuprous cyanide rather than with alcoholic alkali cyanides, with which side reactions such as isomerization and alcoholysis of the double bond are particularly bothersome. With cuprous cyanide the yields in the synthesis of allyl cyanide and methal-lyl cyanide are 84% and 86%, respectively. Higher allylic halides are subject to allylic rearrangements thus cuprous cyanide acts on crotyl halide (CH,CH CHCHjX) and methylvinylcarbinyl halide (CH,CHXCH = CH,) to produce the same mixture of isomeric nitriles (9 1) regardless of which halide is treated. Numerous cyanides of the allylic type (Cj-Ci4) have been prepared, although the possibility of an isomerization has not been considered. A similar isomerization has been observed in the reaction of sorbyl chloride and potassium cyanide. ... 

In this procedure no ptossibility of the formation of water exists at any stage of the reaction. The method has been used for the preparation of several a, olefinic acyl halides from phosphorus oxychloride, although the procedure is said to be less satisfactory than treatment of the free acid with phosphorus trichloride (method 335). ... 

Depending on the solvent, supporting electrolyte, electrode material, and potential, it is possible to electrogenerate either alkyl radicals or carbanions, which can lead to the formation of dimers (R2), alkanes (RH), and olefins [R(-H)]. In addition, the solvent (SH) can act as a hydrogen atom donor or a proton donor. Also olefins can arise from the base-promoted dehydrohalogenation of RX, and other products (RB) can be formed via displacement of halide from RX by a base (B"). When cathode materials such as... 

The transfer of halide from 7r-allylnickel halide to aluminum to give a haloaluminum anion results in a strong decrease in the electron density and formation of free coordination positions on nickel. The presence and number of free coordination positions can be demonstrated by reaction with carbon monoxide. The catalytically active complex, XIII, reacts at —40°C. with 2 moles of carbon monoxide to give the inactive XIV which can be isolated. In XIII, there are accordingly two free coordination positions. During catalysis, these positions are presumably occupied by olefins in the form of 7r-complexes. A stable olefin 7r-complex, 7r-allylnickel (7T-cycloocta-l,5-diene) aluminum tetrabromide, XV, can actually be isolated by adding cycloocta-l,5-diene to a solution of the active complex, XIII. 

Write equations to show how isopropyl alcohol might be prepared (a) from an olefin (b) from an alkyl halide (c) by a Grignard reaction, (d) Which method is used industrially Why ... 

It now appears that olefins prepared from simple alkyl halides are formed with practically no rearrangement of the carbon skeleton. Even with 0-phenylpropyl or jft-phcnylbutyl bromides (XV), systems unusually susceptible to arrangement, the olefins (XVI) were almost entirely of... 

The electron-withdrawing group is absolutely necessary for the acceptance of electron density from a nucleophile. Simple olefinic halides, RCH=CH-X, are very unreactive because there is no good place to put the electrons from the nucleophile. 

Electrochemical reduction of organic halides has attracted considerable attention. Conventional electroreduction on mercury results only in cleavage of the carbon-halogen bond without reduction of unsaturates (52). However, Cd, Zn, Sn, and Cu form also ethane from olefinic halides 370). An EEC mechanism has been proposed for these reductions [i.e., two electrochemical steps (E) and a chemical (C) step, consecutively] involving a direct electron transfer to the halide and formation of a carbanion 32) ... 

Comparison of reactions of halocarbenes, which were produced from either alkylhalodiazirines by nitrogen extrusion, or by the usual method of eliminating hydrogen halide from dihaloalkanes by means of strong bases, bears special interest. Thus phenylchlorocarbene 177 was produced both from benzylidene chloride by potassium-t-butoxide, and by photolysis of phenylchlorodiazirine. ° Competition experiments with mixtures of olefins showed rate differences, especially remarkable for the isobutene-tetramethylethylene pair. The rate proportion was 0.20 when the diazirine... 

A further example of the cyclization of a highly functionalized carbohydrate derivative is given by the preparation of polyhydroxylated cyclopentanes from halogenated carbohydrates19. Treatment of the olefinic halides with tributyltin hydride affords two isomeric products. 

Preparation of Alkyl Halides from Olefins. There are two general methods for the synthesis of alkyl halides (1) by the interaction of an alcohol with a halogen hydride—a procedure that may reasonably be discussed under esterification or halogenation and, also, under the Friedel-Crafts synthesis when a metal halide is used to catalyze the reactions— and (2) by the addition of a halogen hydride to an unsaturated hydrocarbon. This reaction may be catalyzed by metal halides and by sulfuric acid. In the latter instance, the ethylsulfuric acid first formed is converted to the halide by gaseous chlorine or chlorine liberated in situ by action of sulfuric acid on a halide. 

In general, the ease of synthesis of alkyl halides from olefins is dependent on the molecular weights of the hydrocarbons and the particular hydrogen halide. Thus, as was explained earlier in this chapter, the reaction becomes more difficult in passing from iodides through bromides to chlorides. Likewise, olefins containing several carbon atoms react much more readily than those of a lower order. 

There have been several other theories proposed for the mechanism of this reaction where no consideration was given to the existence of addition compounds. Among these may be mentioned the theory of J. U. Nef [Lieb. Ann. 298f 253 (1897)]. He considers that the aluminium chloride splits out the hydrogen halide from the alkyl halide forming in this way an olefin which is added to the aromatic hydrocarbon. This is in line with his views concerning reactions of carbon compounds in general. 

The alcohols may be regarded as a group of compounds similar to the alkyl halides in being olefinates of water in place of acid, just as ammonium hydroxide is an ammoniate of water. The formation of an alkyl halide from an alcohol may therefore be looked upon as the displacement of water by hydrogen halide. 

THE influence OF REACTION CONDITIONS ON THE YIELD OF OLEFINS ARISING FROM SOME ALKYL HALIDES AND SULPHONIUM... 

---