A-Bromo-m-xylene

Dry bromine (405 g. or 2.5 moles) is added to 200 g. (1.9 moles) of m-xylene at 130° over a period of about 6 hours. (Hood.) The resulting product is allowed to stand for 2 days in a vacuum desiccator over solid sodium hydroxide for removal of hydrogen bromide. The product is distilled, and the fraction boiling in the range 110-115°/20 mm. is collected and redistilled to give a 45% yield of a-bromo-m-xylene, boiling at 100-101°/14 mm. 

A solution of 49 g. (0.75 mole) of potassium cyanide in 120 ml. of water and 400 ml. of ethanol is stirred and heated to boiling. Powdered a-bromo-m-xylene (128 g., 0.69 mole) (p. 105) is added as rapidly as the vigorous exothermic nature of the reaction will allow. The reaction mixture is filtered hot, and the filtrate is diluted with 1 1. of water. Extraction with ether followed by drying and distillation of the ethereal solution gives an 85% yield of w-tolylaceto-nitrile boiling at 245-247 /745 mm. The product boils at 133 /15 mm. 

Diacid 54 was prepared by coupling a-a -di-bromo-m-xylene with allylmagnesium chloride, followed by Ru04-mediated cleavage of the resultant diene [29]. Diacid 54, prepared by an alternative route, was already a known compound Ruggli, P. Bucheler, P. Heb. Chim. Acta 1947, 30, 2048. 

Tris-(4-iw-xylyl)stibine 514 4-Bromo-m-xylene (56 g) and antimony trichloride (23 g) are dissolved in dry benzene (150 ml), and then metallic sodium (50 g in pieces) is added. When the reaction is complete (usually after warming) the solution is set aside overnight and then filtered. The residue is extracted three times with boiling benzene. All the liquids are united and the benzene is removed, whereafter the oily residue is poured into anhydrous ethanol. In a few minutes the stibine separates as long needles (25 g, 57 %). 

Yel crysts, mp 206°. Can be prepd by heating 2,4,6-trinitro-5-methoxy-l,3-dimethyl-benzene for 2 hours with ale NH, in a sealed tube on a water bath(Ref 2) or by heating 5-bromo-2,4,6-trinitro-m-xylene with ale NH, at 130 Ref 3)... 

A mixture of 231 g. of the above barium salt and 300 ml. of sulfuric acid (sp. gr. 1.67) is distilled with superheated steam (inlet steam temperature at 200-220° and exit steam at 150-160°). The oily layer of the distillate is separated, washed with water, dried, and distilled twice through a 1-m. packed fractionating column to give 40 g. of o-xylene and 149 g. of l-bromo-2,3-dimethylbenzene, b.p. 210.5-212.5°. This is a 42% yield calculated on the barium salt. 

The recent advances using the relatively cheap and readily available chloroarenes in organometallic chemistry, instead of bromo or iodo-arenes, is arguably one of the most exciting developments in chemistry today [21]. A paper published in 2003 dealt with Heck couplings performed with both activated and deactivated chloroarenes in ionic liquid-doped 1,4-dioxane [145]. The coupling of butyl acrylate and 2-cMoro-m-xylene took 1 h at 180 °C when microwaves were used whereas standard heating at the same temperature required 1.5 h and resulted in a reduced yield (Scheme 15.76). 

Restricted Internal Rotation of Several Symmetric Tops. The tables of thermodynamic functions for an internal rotation of a single symmetric top may be used for several symmetric tops [with moments of inertia calculated from equation (20)] provided both potential energy and kinetic energy cross-terms between the tops can be neglected. Both assumptions have been generally made in calculations for molecules with several tops. Where there are reliable calorimetric data at one or more temperatures, the tables have been used to calculate appropriate potential barriers. Using this procedure thermodynamic contributions have been calculated for propane, 2-methylpropane, 2,2-dimethylpropane, cis-but-2-ene, rm a -but-2-ene, isobutene, o-xylene, > m-xylene, p-xylene, 1,2,3-trimethylbenzene, > 1,2,4-trimethylbenzene, dimethyl sulphide,2-chloro-2-methylpropane, and dimethyl-amine. In several cases thermodynamic contributions have been calculated using potential barriers estimated from those of related molecules. Examples of this procedure are found in calculations for 2-fluoro-2-methylpropane, 2-chloropropane, 2-bromopropane, 2-iodopro-pane, 2,2-dichloropropane, 2-bromo-2-methylpropane, 2-iodo-2-methylpropane, 1,3,5-trimethylbenzene, 1,2,3,5-tetramethylbenzene, 1,2,4,5-tetramethylbenzene, 1,2,3,4-tetramethylbenzene, pentamethyl-benzene, and hexamethylbenzene. ... 

Stock and Baker2 5 9 measured the relative rates of chlorination of a number of halogenated aromatics in acetic acid containing 20.8 M H20 and 1.2 M HC1 at 25 °C and the values of the second-order rate coefficients (103Ar2) are as follows p-xylene (11,450), benzene (4.98), fluorobenzene (3.68), chlorobenzene (0.489), bromobenzene (0.362), 2-chlorotoluene (3.43), 3-chlorotoluene (191), 4-chloro-toluene (2.47), 4-fluorotoluene (9.70), 4-bromotoluene (2.47). Increasing the concentration of the aromatic, however, caused, in some cases, a decrease in the rate coefficients thus an increase in the concentration of chlorobenzene from 0.1 M to 0.2 M caused a 20 % decrease in rate coefficient, whereas with 4-chloro-and 4-bromo-toluene, no such change was observed. 

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