Cyclohexyl, bromide

Both have reasonable mechanisms, but we prefer (b) because it introduces more simphfication. Route (a) simply ehops off one carbon atom and leaves us with a new target almost as difficult to make as TM 16. Route (b) however breaks the molecule into two more equal pieces -acetone and cyclohexyl bromide. 

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... 

Further insight into the E2 mechanism comes from stereochemical studies One such experiment compares the rates of elimination of the cis and trans isomers of 4 tert butyl cyclohexyl bromide... 

Cyclohexyl bromide Potassium ethoxide Cyclohexene Ethanol... 

Cyclohexyl bromide is less reactive than noncychc secondary alkyl halides toward 8 2 sub stitution Construct a molecular model of cyclohexyl bromide and suggest a reason for its low reactivity... 

A 3-I. three-necked, round-bottom flask is fitted with a mechanical stirrer through a mercury seal, a reflux condenser and a i-l. separatory funnel. A mixture of 200 g. (r mole) of 2,3-dibromopropene (Org. Syn. 5, 49) and 200 cc. of dry ether is added. The flask is now cooled in an ice bath, the stirrer is started, and one molecular equivalent of cyclohexylmagnesium bromide, prepared from 31 g. of magnesium, 204 g. of cyclohexyl bromide and 400 cc. of dry ether (Note i) is added at such a rate that the mixture refluxes gently (Note 2). The addition takes about one-half to three-quarters of an hour. Two layers are formed and magnesium bromide may or may not separate. 

The preparation of cyclohexylmagnesium bromide is described on p. 22. The solution may be standardized by titrating against 0.5 N hydrochloric acid, and exactly one mole equivalent is used in the preparation. Five cubic centimeters of cyclohexylmagnesium bromide solution is slowly added to 20 cc. of water, an excess of the standard acid is added, and the excess acid titrated with sodium hydroxide. If 85 g. (3.5 moles) of magnesium, one liter of dry ether, and 571 g. of cyclohexyl bromide (3.5 moles) are used, a solution results which is about 2 molar. 

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. 

If the cyclohexyl bromide contains traces of alcohol the yield is considerably reduced. The alcohol may be removed by washing with cold concentrated sulfuric acid, then with water, and finally drying and distilling. 

Cyclohexyl bromide [108-85-0] M 156.3, b 72 /29mm, d 0.902, n 1.4935. Shaken with 60% aqueous HBr to remove the free alcohol. After separation from excess HBr, the sample was dried and fractionally distd. 

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. 

Ethy I-p-hydroxy benzoate Cyclohexyl bromide 3-(2 -Methylplperidino)propyl chloride... 

Hydroxyprogesterone caproate Cyclohexylacetone Droprenilamine HCl Propylhexedrine Cyclohexylamine Clorexolone Cyclamate calcium 1 -Cyclohexylamino-2-propanol Hexylcaine HCl Cyclohexyl bromide Cetiedll... 

Cyclohexen-l-one, 3-methyl-, 53, 101 Cyclohexyl bromide [Cyclohexane, bromo ], 82... 

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