Question

1. Procedure A. Lithium 2,6-dimethylphenoxide. In a 300-ml. flask, equipped with a magnetic stirrer and a reflux condenser and flushed with nitrogen, are placed 150 ml. of toluene (freshly distilled from sodium), 1.40 g. (0.202 mole) of lithium metal (Note 1) and 25.0 g. (0.205 mole) of resublimed 2,6-dimethylphenol. The mixture is heated under reflux with stirring for 36 hours; a nitrogen atmosphere is maintained for the reflux period (Note 2). The condenser is replaced by a distillation head with a condenser set for distillation, and a distillation capillary is inserted in the thermometer joint. The bulk of the toluene is removed under nitrogen at reduced pressure (Note 3). The distillation head is rapidly removed, and the flask is flushed with nitrogen and closed by a stopper. The stoppered flask is transferred to a dry box flushed with nitrogen, the stopper removed, and the slurry in the flask filtered with suction through a 65-mm. sintered-glass funnel. The collected lithium salt is washed with three 75-ml. portions of hexane (freshly distilled from lithium aluminum hydride), and the white powder (Note 4) is dried at 100-150° and 0.5 mm. pressure to constant weight (3-10 hours is required). The yield of lithium 2,6-dimethylphenoxide as a fine white or light gray powder is 25.0-25.5 g. (98-100%) (Note 5) and (Note 6). B. 2,6, 6-Trimethyl-2,4-cyclohexadienone. In a nitrogen-filled dry box, 25.0 g. of lithium 2,6-dimethylphenoxide (0.195 mole) is transferred to an oven-dried, thick-walled Pyrex® bomb tube (650 x 19 mm.). The bomb tube is stoppered with a rubber stopper fitted with a drying tube, removed from the dry box, and 75 ml. of methyl iodide (170 9., 1.20 moles) (freshly distilled from calcium hydride) is quickly pipetted into the bomb under a dry nitrogen stream. The bomb is cooled in a dry-ice bath and sealed with an oxygen torch. After warming to room temperature, the bomb is shaken to disperse the salt cake and placed in a bomb furnace which has been preheated to 1350 (Note 7). After 36 hours the furnace is allowed to cool, the bomb is removed, cooled to dry-ice temperatures, and opened carefully as there may be residual pressure. The golden brown liquid is poured into a 200-ml. flask, and the methyl iodide is removed on a rotary evaporator Caution! (Hood). The residue from the flask and the bomb is washed into a 500-ml. separatory funnel with 100 ml. each of ether and 1:1 solution of Claisen's alkali and water (Note 8). The funnel is shaken, and the alkali layer is removed. The ether layer is extracted four additional times with 100 ml. portions of the alkali (Note 9), washed twice with 75-ml. portions of water, once with saturated aqueous salt solution, and dried by filtration through anhydrous sodium sulfate into a 200-ml. round-bottomed flask. The ether is removed on a rotary evaporator, and the 23.0 g. of yellow oil remaining is allowed to stand at room temperature for 7-10 days to permit dimerization of the dienone (Note 10). The 2,6-dimethylanisole is removed by vacuum distillation (nitrogen capillary bubbler) at 35-50° (0.75 mm. or less pressure). The solid dimerized product2 in the residue is either recrystallized twice from the minimum amount of hot hexane or vacuum-distilled, b.p. 175° (25 mm.) (Note 11) followed by a single recrystallization from hexane. The yield of purified 2,6,6-trimethyl-2,4-cyclohexadienone dimer (white needles, m.p. 119.5-121.09) is 4.8-5.1 g. (18-19%) (Note 12), and the yield of 2,6-dimethyl anisole is 13.5-14.0 g. (51-53%). The dienone monomer may be regenerated from its dimer as desired by heating the dimer above 170° for several minutes in a test tube and quenching, or by distillation at 25 mm. (Note 11) through a short condenser into a dry ice-acetone cooled receiver. The monomer may be stored for several days at dry-ice temperatures without appreciable dimerization.

Answer 1

based on the procedure given above, 27.7g is the theoritical yield of the product. which means, 0.0203moles of the product was synthesised.

for synthesis of 750 mg (ie 0.0055 moles) of the product, assuming that the mm of the product is 136.19g, we need o.o528 moles of the reactant a. this gives us the amount req of reactant a ie, 6.7g. now if 25g of reactant a reacts with 170g of reactant b, it nmeans, abount 45. 56 g of reactant b will be req to react with 6.7g of reactant a. therefore, for 750mg of the desired product, start with 6.7g of reactant a and 45.56g of reactant b.

to make sure the yield is 80%, keep in mind that the pot temperature should be maintained at 175–200° to reverse the dimerization.