Cholesterol bromination

Cholestanol, cholesterol Apply sample solution, treat with a 2 to 3-fold excess of 0.1% bromine in chloroform. Only cholesterol is derivatized. [45]... 

Unsubstituted solid alicyclic alkenes have also been exposed to bromine vapor and gave 100% of pure trans dibromides, as in the case of cholesterol (123) [75] and the (milled) exo adduct 1 [22] (Scheme 14). The products 124 and 125 cannot be obtained with the same good quality from solution reactions. 

A. Cholesterol dibromide. In a 4-1. beaker 150 g. (0.39 mole) of commercial cholesterol (Note 1) is dissolved in 1 1. of absolute ether by warming on the steam bath and stirring with a stout glass rod the solution is then cooled to 25°. A second solution is prepared by adding 5 g. of powdered anhydrous sodium acetate (0.06 mole) (Note 2) to 600 ml. of acetic acid, stirring the mixture and breaking up the lumps with a flat stirring rod 68 g. (0.4 mole) of bromine is then added, and the solution is poured with... 

Purification of cholesterol through the dibromide completely eliminates cholestanol, 7-dehydrocholesterol, and latho-sterol (A7-cholestenol). The first crop of material from methanol-ether is also free from cerebrosterol (24-hydroxycholesterol) and 25-hydroxycholesterol, a product of autoxidation present in cholesterol that has been stored in the crystalline state for a few years with access to air. When material of highest purity is desired, only first-crop dibromide should be employed, since de-bromination of second-crop material gives sterol melting at 146-147° and giving a positive Beilstein test. 

Cholesterol dibromide has been prepared by unbuffered 2 and buffered 3 bromination of cholesterol and oxidized to 5with acid permanganate,2 chromic acid,4 6 6... 

Similar, shielding, y-gauche effects are evidenced at carbons 9 and 14 when a 7ct-hydroxy (compound 414) or a 7cr-hydroperoxy (compound 416) group is substituted into cholesterol (compound 211). The effects of bromine, hydroxyl, and hydroperoxy are —6 to —7 ppm for groups without hydrogen or with hydrogen and certainly of differing physical size. 

The addition of bromine and chlorine azide to unsaturated steroids is generally diastereoselective, when both the simple and induced diastereoselectivity are considered. In fact, a single enantiomer was obtained from 5a-cholest-2-ene (8)35,36, cholesterol (9)51, and progesterone (10)52 (in this case with undetermined configuration). Testosterone esters, however, afforded mixtures of stereoisomers52. 

Dehydrocholesterol has also been made from cholesterol by the Windaus procedure (Fig. 2) the 3,7-dibenzoate (16) is obtaiaed (via (14) and (15) by oxidation and reduction), which undergoes thermal elimination to give the 7-dehydrocholesteryl benzoate (11) (42—44). However, the yields are substantially lower than those achieved by the bromination—dehydrobromination method. 

Tosylhydrazone and 7-phen)d sulfoxide groups have also been introduced into cholesterol and eliminated to prepare the 5,7-diene (45,46). The method of choice is the allyUc bromination—dehydrobromination procedures, and the commercial yields in converting cholesterol to 7-dehydrocholesterol... 

Prelab Exercise Explain how the process of bromination and debromination of cholesterol can free it from impurities. Write a detailed mechanism for the bromination of cholesterol, taking care to consider the stereochemistry of the product. 

The bromination of a double bond is an important and well-understood organic reaction. In the present experiment it is employed for the very practical purpose of purifying crude cholesterol through the process of bromination, crystallization, and then zinc dust debromination. 

Cholesterol isolated from natural sources contains small amounts (0.1-3%) of 3)3-cholestahol, 7-cholesten-3/3-ol, and 5,7-cholestadien-3/3-ol. These are so very similar to cholesterol in solubility that their removal by crystallization is not feasible. However, complete purification can be accomplished through the sparingly soluble dibromo derivative 5a,6/3-dibromocholestan-3/3-ol. 3/3-Cholestanol is saturated and does not react with bromine thus, it remains in the mother liquor. 7-Cholesten-3/3-ol and 5,7-cholestadien-3j8-ol are dehydrogenated by bromine to dienes and trienes, respectively, that likewise remain in the mother liquor and are eliminated along with colored by-products. 

Why does not acetate ion attack the intermediate bromonium ion to give the 5-acetoxy-6-bromo compound in the bromination of cholesterol ... 

The commercial material is normally obtained from the spinal cord of cattle by extraction with petroleum ethers, but it may also be obtained from wool fat. Purification is normally accomplished by repeated bromination. Cholesterol may also be produced by entirely synthetic means. ... 

The reactions of ethylene and cholesterol with bromine. In both molecules, electrostatic potential maps show similar charge patterns for the carbon-carbon double-bond functional group. Bromine therefore reacts with both in exactly the same way. The size and complexity of the remainders of the molecules are not important. 

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