2- benzene-, lithium

Klumpp and Sinnige proceeded similarly, using ec-butyl alcohol to protodelithi-ate the anisoles and other lithiated aryl ethers in di-n-butyl ether. The protodelithiation enthalpies for all the lithiated aryl ethers, as monomers, from the latter study are listed in Table 3. The reaction enthalpies for the o- and p-lithioanisoles are ca 20 kJmop more negative from Reference compared to the ones from Reference, presumably due to differences in the reaction media. From the exchange reaction, equation 17, and the enthalpies of formation of phenyl lithium, benzene and the relevant aryl ether, the enthalpies of formation of the lithiated aryl ethers can be derived. The calculated values are shown in Table 3. 

The authors of ref. 46. reported flow times for polystyryl-lithium-benzene solutions before and after the addition of diphenyl ether whereupon the active centers were terminated and the flow times again measured. Table III of the note in question (46) says that in pure benzene, Nw, is 1.96 and 2.0 —in apparent agreement with the generally held belief that polystyryllithium is exclusively dimeric in benzene. Following the addition of diphenyl ether to achieve the specified concentration (0.15M), the authors in their Table III then reported values of Nw of 1.88 and 1.95 (based on their flow times ). From these values, it was concluded that diphenyl ether does not influence the association state of polystyryllithium. 

The effects of added species. The rate of nitration of benzene, according to a rate law kinetically of the first order in the concentration of aromatic, was reduced by sodium nitrate, a concentration of io mol 1 of the latter retarding nitration by a factor of about Lithium nitrate... 

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

Synthesis by high-dilution techniques requires slow admixture of reagents ( 8-24 hrs) or very large volumes of solvents 100 1/mmol). Fast reactions can also be carried out in suitable flow cells (J.L. Dye, 1973). High dilution conditions have been used in the dilactam formation from l,8-diamino-3,6-dioxaoctane and 3,6-dioxaoctanedioyl dichloride in benzene. The amide groups were reduced with lithium aluminum hydride, and a second cyclization with the same dichloride was then carried out. The new bicyclic compound was reduced with diborane. This ligand envelops metal ions completely and is therefore called a cryptand (B. Dietrich, 1969). 

The equihbrium shown in equation 3 normally ties far to the left. Usually the water formed is removed by azeotropic distillation with excess alcohol or a suitable azeotroping solvent such as benzene, toluene, or various petroleum distillate fractions. The procedure used depends on the specific ester desired. Preparation of methyl borate and ethyl borate is compHcated by the formation of low boiling azeotropes (Table 1) which are the lowest boiling constituents in these systems. Consequently, the ester—alcohol azeotrope must be prepared and then separated in another step. Some of the methods that have been used to separate methyl borate from the azeotrope are extraction with sulfuric acid and distillation of the enriched phase (18), treatment with calcium chloride or lithium chloride (19,20), washing with a hydrocarbon and distillation (21), fractional distillation at 709 kPa (7 atmospheres) (22), and addition of a third component that will form a low boiling methanol azeotrope (23). 

Alkali Metal Catalysts. The polymerization of isoprene with sodium metal was reported in 1911 (49,50). In hydrocarbon solvent or bulk, the polymerization of isoprene with alkaU metals occurs heterogeneously, whereas in highly polar solvents the polymerization is homogeneous (51—53). Of the alkah metals, only lithium in bulk or hydrocarbon solvent gives over 90% cis-1,4 microstmcture. Sodium or potassium metals in / -heptane give no cis-1,4 microstmcture, and 48—58 mol % /ram-1,4, 35—42% 3,4, and 7—10% 1,2 microstmcture (46). Alkali metals in benzene or tetrahydrofuran with crown ethers form solutions that readily polymerize isoprene however, the 1,4 content of the polyisoprene is low (54). For example, the polyisoprene formed with sodium metal and dicyclohexyl-18-crown-6 (crown ether) in benzene at 10°C contains 32% 1,4-, 44% 3,4-, and 24% 1,2-isoprene units (54). 

Ethereal methyl1ithiurn (as the lithium bromide complex) was obtained by the submitters from Aldrich Chemical Company Inc. The checkers used 1.19 M methyl1ithiurn-lithium bromide complex in ether supplied by Alfa Products, Morton/Thiokol, Inc. The concentration of the methyllithium was determined by titration with 1.0 M tert-butyl alcohol in benzene using 1,10-phenanthroline as indicator. The submitters report that ethereal methyllithium of low halide content purchased from Alfa Products, Morton/Thiokol, Inc., gave similar results. 

In the flask is placed 150 ml. of anhydrous ether, and 5.7 g. (4.1 atomic equivalents) of lithium foil is then added (Note 1). A solution of 56.6 g. (0.2 mole) of n-bromoiodobenzene in 300 ml. of anhydrous ether is added dropwise (Note 2). When a vigorous reaction commences, the stirrer is started and the flask is cooled in ice water to maintain the temperature at about lO. The reflux condenser is replaced by a thermometer, and the remainder of the n-bromoiodobenzene solution is added at a rate such that the temperature in the flask remains at about 10° (about 1.5 hours). When this addition is complete, 200 ml. of dry benzene is added the mixture is stirred at 10° for 1 hour and finally at room temperature for 1 hour. The mixture is then poured through a glass-wool filter on 200 g. of ice. 

Kyba and eoworkers prepared the similar, but not identical compound, 26, using quite a different approach. In this synthesis, pentaphenylcyclopentaphosphine (22) is converted into benzotriphosphole (23) by reduction with potassium metal in THF, followed by treatment with o "t/20-dichlorobenzene. Lithium aluminum hydride reduction of 23 affords l,2-i>/s(phenylphosphino)benzene, 24. The secondary phosphine may be deprotonated with n-butyllithium and alkylated with 3-chlorobromopropane. The twoarmed bis-phosphine (25) which results may be treated with the dianion of 24 at high dilution to yield macrocycle 26. The overall yield of 26 is about 4%. The synthetic approach is illustrated in Eq. (6.16), below. 

Lithium metal in ammonia at high concentration (4 M), with an alcoholic proton donor, will reduce the benzene ring of a phenoxide ion. The lithium salt of estrone is reduced under such conditions in 95% yield to a mixture containing 77% of estr-5(10)-ene-3a,17i -diol and 23% of the derived 5(10)-dihydro derivative. 

Krapcho and Bothner-By made additional findings that are valuable ii understanding the Birch reduction. The relative rates of reduction o benzene by lithium, sodium and potassium (ethanol as proton donor) wer found to be approximately 180 1 0.5. In addition, they found that ben zene is reduced fourteen times more rapidly when methanol is the protoi donor than when /-butyl alcohol is used. Finally, the relative rates of reduc tion of various simple aromatic compounds by lithium were deteiTnined these data are given in Table 1-2. Taken together, the above data sho that the rate of a given Birch reduction is strikingly controlled by the meta... 

A cold (0°) solution of 15 g (0.039 mole) of cholest-4-en-3-one, mp 79-80°, in 200 ml of ether-benzene (8 1) is added dropwise to 0.05 mole of lithium tri-t-butoxyaluminum hydride in ether-diglyme at —40° to —50°. The mixture is allowed to stand overnight at 0° and then hydrolyzed by treatment with ice, 5 N sodium hydroxide and Rochelle salt. Evaporation of the washed and dried ether extracts and crystallization of the residue from ethyl acetate affords 13 g (87 % yield) of nearly pure cholest-4-en-3j9-ol, mp 126-129°. One recrystallization from the same solvent gives the pure product as large needles mp 131-132°, [a]o 46° reported mp 132° [a]c, 44° (benzene). 

To 1 g of 2j5-azido-3a-iodo-5a-cholestane ° in 10 ml benzene is added 0.4 g trimethyl phosphite. A boiling chip is added and the mixture allowed to stand at room temperature for 4 days. The solvent is removed in vacuo, with most of the trimethyl phosphite being removed at 0.1 mm. This crude product (100) is dissolved in 10 ml of dry ether and added dropwise to a stirred mixture of 0.5 g of lithium aluminum hydride in 10 ml of ether. After stirring at 25° for 3 hr, the excess of hydride is destroyed by the addition of 2 ml 20 % sodium hydroxide and the aluminum salts are filtered. The solution is washed with ether, and the ether removed in vacuo giving 0.71 g [76 %] of product (95) mp 101-103°. 

To a solution of 0.5 g of lithium aluminum hydride in 35 ml of ether is added 0.2 g of the A -cyanoaziridine. The mixture is heated at reflux temperature for 3.5 hr, cooled, and treated with excess saturated sodium sulfate in water. Filtration and evaporation of the ethereal filtrate gives 0.18 g of a glass which is chromatographed on 10 g of basic alumina (activity III). The benzene-petroleum ether (1 3) eluate gives 0.12 g of 2a,3a-imino-5a-choles-tane, mp 117.5-118.5°, after crystallization from methanol. 

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