Cyclohexyl bromide, reaction

Assuming that the rate determining step in the reaction of cyclohexanol with hydrogen bro mide to give cyclohexyl bromide is unimolecular write an equation for this step Use curved arrows to show the flow of electrons... 

In a i-l. three-necked, round-bottom flask fitted with a mechanical stirrer through a mercury seal, a separatory funnel and an efficient reflux condenser to which a calcium chloride tube is attached, are placed 25 g. (1.03 moles) of magnesium turnings 140 cc. of dry ether, and a small crystal of iodine. The stirrei is started and a small portion (about 10 cc.) of a solution of 118.5 g. (i mole) of cyclohexyl bromide (Note i) in 120 cc. of dry ether is added through the separatory funnel. After the reaction starts, the remainder of the solution is run in at such a rate that the whole is added at the end of forty-five minutes. The mixture is stirred and refluxed for an additional thirty to forty-five minutes. 

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. 

By studying the NMR spectra of the products, Jensen and co-workers were able to establish that the alkylation of (the presumed) [Co (DMG)2py] in methanol by cyclohexene oxide and by various substituted cyclohexyl bromides and tosylates occurred primarily with inversion of configuration at carbon i.e., by an 8 2 mechanism. A small amount of a second isomer, which must have been formed by another minor pathway, was observed in one case (95). Both the alkylation of [Co (DMG)2py] by asymmetric epoxides 129, 142) and the reduction of epoxides to alcohols by cobalt cyanide complexes 105, 103) show preferential formation of one isomer. In addition, the ratio of ketone to alcohol obtained in the reaction of epoxides with [Co(CN)5H] increases with pH and this has been ascribed to differing reactions with the hydride (reduction to alcohol) and Co(I) (isomerization to ketone) 103) (see also Section VII,C). 

In nucleophilic solvents, products that arise from reaction of the solvent with the cationic intermediate may be formed. For example, reaction of cyclohexene with hydrogen bromide in acetic acid gives cyclohexyl acetate as well as cyclohexyl bromide. This occurs because acetic acid acts as a nucleophile in competition with the... 

Reaction of 1,4-Dilithiated Isopropen ytacefylene with Oxirane and Cyclohexyl bromide... 

So the synthesis could be done in one step by making the anion of methyl acetate and reacting it with bromocyclohexane. The polarities of the reaction partners match nicely, but the problem is that alkylations of secondary bromides with enolates often give poor yields. The enolate is a strong base, which promotes elimination in the secondary bromide rather than giving the substitution product needed in the synthesis. Thus elimination from cyclohexyl bromide to cyclohexene would be a major process if the reaction were attempted. While the retrosynthetic step seems reasonable, the synthetic step has known difficulties. It is important to work backward in the retrosynthetic analysis and then check each forward step for validity. 

Data assembled by Parker (201 demonstrate these effects for bimolecular reactions involving sulfur nucleophiles and haloaliphatic substrates. As an illustration for the case of Reactions 4, the S 2 displacement of iodide from CH3I by SCN at 25°C is accelerated relative to its rate in water tty 0.2 log units in methanol, by 1.1 log units in 10% aqueous dimethyl sulfoxide (v/v), and tty approximately 2.4 log units in dimethyl formamide (DMF). Furthermore, the rates of bimolecular elimination and substitution of cyclohexyl bromide in the presence of thiophenolate at 25°C both increase by 2.7 log units when the solvent is changed from ethanol to dimethylfonnamide (20). 

In a 100 ml flask fitted with a mechanical stirrer, a vertical condensor protected by a calcium chloride stopper, a dropping-funnel and a source of nitrogen were introduced 30 ml of hexamethylenephosphotriamide and 2.3 g (0.1 mol) of finely cut sodium wire. A mixture of 12.3 g (0.1 mol) of (3-thienyl)-acetonitrile and 16.3 g (0.1 mol) of cyclohexyl bromide was then quickly added at a temperature of 20 C. The reaction mixture was then maintained under nitrogen atmosphere and stirred for 12 hours at room temperature. The excess of sodium was destroyed by adding 5 ml of ethanol and the organic solution was slowly poured into 100 ml of a 1 N iced solution of hydrochloric acid. The solution was extracted twice with 100 ml ether. The ethereal phases were collected, washed with water, dried and concentrated under reduced pressure. The crude product was then purified by... 

Refluxing treatment of a mixture of cyclohexyl bromide and Bu3SnH in the presence of a catalytic amount of 2,2 -azobis (isobutyronitrile) (AIBN) in benzene produces cyclohexane in good yield as shown in Scheme 1.6. The Bu3SnH/AIBN system is the most popular radical reaction system in organic synthesis. 

A dark reaction accelerated by light was observed with cyclohexyl bromide (81b). / -DNB did not affect the dark reaction while it partially inhibited the photostimulated one. The results suggest that 81b reacts, under irradiation, mostly by the S l mechanism. The dark reaction may be due to a polar or an ET reaction through cage collapse54 151. 

We must assume that this holds even for simple unsubstituted cyclohexanes, and that substitution reactions of cyclohexyl bromide, for example, occur mainly on the minor, axial conformer. This slows down the reaction because, before it can react, the prevalent equatorial conformer must first flip axial. 

Why is it difficult for cyclohexyl bromide to undergo an E2 reaction When it is treated with base, it does undergo an E2 reaction to give cyclohexene. What conformational changes must occur during this reaction ... 

In an attempt to clarify the situation the rotating cryostat has been used to prepare cyclohexyl radicals in a variety of matrices by the reaction of cyclohexyl bromide with sodium. The radicals were allowed... 

The use of water, which has strong OH-bonds, should eliminate hydrogen abstraction from the matrix. However, the yield of cyclohexane was still higher than that of cyclohexene. This result can be attributed to the formation of hydrogen atoms by reaction of some alkali metal atoms with water instead of with cyclohexyl bromide. These hydrogen atoms could then either combine with cyclohexyl radicals to give cyclohexane or add to cyclohexene (formed from a previous disproportionation reaction) to regenerate cyclohexyl radicals. 

The synthetic equivalent for the cyclohexyl carbocation is cyclohexyl bromide. Thus, cyclohexanol can be prepared by the reaction of cyclohexyl bromide with hydroxide ion. 

Although alkylation reactions of pseudoephedrine amide enolates are successful with a broad range of electrophiles, a few problematic substrates have been identified. Among these are secondary alkyl halides, such as cyclohexyl bromide, and alkyl halides that are both (3-branched and (3-alkoxy substituted. However, there is evidence that the thermal stability of pseudoephedrine amide enolates may be such that extended reaction times at ambient temperature, or even heating, may be tolerated ... 

The presence of unsymmetrical dialkyl ditcllurium and unsymmetrical diaryl ditellurium" compounds in solution was confirmed by Te-NMR spectroscopy H-NMR spectroscopy , and mass spectroscopy . Cyclohexyl methyl ditellurium was claimed to have been isolated from a reaction mixture obtained by sequential addition of cyclohexyl bromide and methyl iodide to a solution of tetratelluride anions in dimethylformamide . The chromophoric Te —Te group in the aliphatic and aromatic ditellurium compounds imparts a characteristic orange to red color caused by an absorption maximum at approximately 400 nm. Most of the aromatic ditellurium derivatives are stable as solids toward atmospheric agents, but oxidize slowly when dissolved. The short-chain aliphatic ditellurium compounds are distillable red liquids having an obnoxious odor that clings to skin and clothes. Ditellurium compounds with more than ten carbon atoms in each aliphatic group are low melting solids that can be handled in air. 

The reactions with cyclohexyl bromide and phenacyl bromide were carried out without solvent while the reaction with hexadecyl chloride was performed in dimethylformamide lodobenzene did not react with tellurium. lodopentafluorobenzene reacted to produce bis pentaJiuorophenyl] tellurium. ... 

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