Preparing Cold Baths

The present procedure represents a modification of two previously published procedures,2 3 and results in a safer, more convenient preparation of the title compound. In Step A, the ratio of reagents has been adjusted to allow for the formation of only pentaerythrityl tetrachloride and trichlorohydrin none of the dichlorinated product is produced. Thus work up of the reaction is easier the product can be filtered rather than extracted, so minimal solvent is used, and the crude products are used in Step B, thus avoiding a tedious distillation. Step B has also been modified to make it safer and more convenient. The crude material from Step A is used, and addition of nitric acid over a longer period reduces the hazards of this step. Previously, it was noted that after the nitric acid was added in one portion and the mixture was heated, "a reaction became apparent, whereupon the flask was lowered rapidly into a waiting cold bath and the operator withdrew. 2 Step C is a more detailed modification of the procedure reported by the Russian workers3 as an improvement to the original method of Mooradian and Cloke.2 The latter used quinoline to catalyze the conversion of tris(chloromethyl)acetic acid to 3-chloro-2-(chloromethyl)propene. 

Cryogenic materials and the surfaces they cool can cause severe cold bums if they are allowed to contact the skin. Thick gloves and a face shield may be needed when preparing or using some cold baths. 

Take an oven-dried three-necked round-bottomed flask (250 mL) and add the tetratoluenesulfonamide (1.96 g, 2,04 mmol), prepared as described in step 15, under a positive pressure of nitrogen. Equip the flask with a dry ice condenser, a nitrogen inlet and a stopper, and add dry tetrahydrofuran (30 mL) and dry ethanol (2 mL). Cool the suspension in a dry ice/ isopropanol cold bath and add dry ice and isopropanol to the dry ice condenser. Allow ammonia gas (from a cylinder) to condense into the cooled flask until about 75 mL of liquid ammonia has been added. 

Pyridin-4-amine (5 10 g, 0.11 mol) was added to I IBF,j [prepared from 40% hydrofluoric acid (42 mL)]. The solution was stirred and cooled in an ice-salt bath. NaNO (7.5 g. 0.11 mol) was added in portions within 30 min and stirring was continued for an additional 10 min. The cold bath was removed and the diazonium salt was allowed to decompose. The solution was stirred and cooled to — 20 C. then cold 70% aq K.OH (20 mL) was added in one portion. After purification the colorless title compound was obtained yield 2.3 g (22%). 

A mixture of freshly prepared, cold cyclopentadiene (3.3 g. 0.05 mol) and condensed 3.3,3-trifluoropropene (1 4.8 g, 0.05 mol) was combined with hydroquinone (0.05 g) in a heavy-walled Pyrex tube at —78 C. The lube was sealed and heated in a 135 C oil bath behind a safety shield for 84 h. Afler cooling to — 78 C, ihc tube was opened. A small amount of volatile material boiled away upon warming to rt. w hereupon the cloudy liquid was transferred to a slill equipped wilh a 10-cm Vigreux column. Distillation at 130 Torr gave the product as a colorless liquid at 66 C yield 5.66 g (70%). 

To prevent the condensation of water into your flask, you should have an inert gas flowing through it (see p. 126) and prepare the cold bath around the flask and its contents so that slow cooling occurs. Sudden immersion of a relatively hot flask into the cold bath will cause the bath to boil and air (containing water vapour) will be sucked into the apparatus despite the inert atmosphere. Alternatively a loosely packed CaCb guard tube (see p. 117) will suffice if cooling is not too rapid. 

To a solution of 25.27 g (102.3 mmol) of [ClPNCHMe2]2 in 50 mL of diethyl ether a solution of 102.3 mmol of (Me3Si)(Me2CH)NLi [prepared from 13.42 g (18.9 mL, 102.3 mmol) of (Me3SiXMe2CH)NH in 50 mL of diethyl ether and 102.3 mmol of n-butyllithium in hexane] is added dropwise (30 min) with magnetic stirring at -16° (ice-sodium chloride mixture). [Note The stoichiometry must be exact even a small excess of LiN(i-Pr)TMS induces decomposition.] After removal of the cold bath the reaction mixture is stirred for 45 min at room temperature and reduced in volume to approximately 50 mL. Lithium chloride is filtered off (D4 frit) and washed twice with 10 mL of pentane. The solvent is removed under reduced pressure (0.01 torr) to yield 33.1 g (95%) of an orange-brown oil (crude). 

A) Preparation of Benzalacetophenone (Sm.). Place in an eight-inch tube a solution of 1 g of sodium hydroxide in 8 ml of water and 6 ml of alcohol. Cool in an ice-salt mixture. Add 2.6 g of acetophenone (2.6 ml) shake well, and immerse again in the cold bath. Add 2.3 g (2.2 ml) of freshly distilled pure benzaldehyde, close tube with a solid rubber stopper, and shake vigorously. Allow... 

A) Preparation of Benzidine (Sm.). Prepare about 2 g of hydrazobenzene according to Experiment 30. Dissolve in a small flask 2 g of hydrazobenzene in 15 ml of ether. Place 8 ml of concentrated hydrochloric acid and 8 ml of water in an eight-inch test tube and provide with solid rubber stopper. Cool in an ice-salt mixture. Add the ethereal solution slowly by means of a dropper to the cold diluted acid, and shake vigorously after each addition. When all the hydrazobenzene solution has been added, allow to stand 10 minutes, and add 10 ml of concentrated hydrochloric acid. Allow the tube to remain in the cold bath 15 minutes longer. Filter the benzidine hydrochloride with suction. Wash the crystals with 5 ml of dilute (1 1) hydrochloric acid and finally with two 5 ml portions of ether, and dry on a paper disc. The yield is about 2 g. 

If the reaction does not start at once, lower the ice bath, and introduce a rod in the tube and cautiously break the acetanilide adhering to the tube. Replace the cork, and use the cold bath to moderate the reaction if it is too vigorous. When most of the acetanilide has dissolved, place a beaker with water under the tube and heat at 80-90° for 15 minutes. Cool, and pour very slowly, with stirring, into a mixture of 50 g of ice and 50 ml of water. This operation should be performed in the hood and goggles should be worn. Rinse the reaction tube with 10 ml of water, and unite with the main portion. After 10 minutes filter the mass, breaking any lumps that may have formed. Wash with three 5 ml portions of water, press the cake to drain the water as much as possible, and use directly for the next preparation. 

Prepare a diazotizing bath by dissolving 10 cc. of concentrated hydrochloric acid in 500 cc. of cold water and then adding 0.2 gram of sodium nitrite. Place in the bath the three pieces of cloth which have been dyed with primuline, and allow them to stay 10 minutes. Stir occasionally. Prepare three baths in which the diazotized primuline is to be developed. Dissolve 0.1 gram p-naphthol in 1 cc. of a 10 per cent solution of sodium hydroxide, and add 100 cc. of water dissolve 0.1 gram resorcinol... 

Preparation of L3-Bisrdimethylhydrogensilylmethylene benzene. To a N2 purged round bottom flask in a cold bath at -40°C was added 100 mL of THF. To the THF was added 9.0 mL of chlorodimethylsilane (81 mmol). The dianion of m-xylene (20 mmol) was taken and the hexane layer was removed. To each centrifuge tube was added 20 mL of THF with shaking. After the anions were suspended in the THF, the contents of each one was slowly added to the round bottom flask. The reaction was allowed to proceed for 5 h after the final addition of the anion. After 5 h, the solution was washed with a saturated NaCl solution. To the organic layer which separated was added hexane or diethyl ether which forced out a second aqueous layer. The organic phase was dried over magnesium sulfate and... 

The P-naphthylamine hydrochloride (0,4 mole) was stirred overnight in a mixture of 100 mL of water and 120 mL of HCl and then diazotized with 28 g of NaN02 dissolved in 60 mL of water at -5 to -8 C using a cold bath of dry ice and o-xylene. The sodium salt of nitromethane was prepared in a separate vessel by combining 0.4 mole (22 mL) of nitromethane in 100 mL of absolute ethanol with 16 g of NaOH in 100 mL of wato- at -5 to -8 C. The resulting white precipitate of the sodium salt of nitromethane was dissolved in 50 mL of water to give a yellow solution. This solution was added dropwise to the filtered diazonium salt solution kept at -8 C. The final mixture was stirr for 3 hr. The precipitate was filtered off and washed with water. The crude product was purified by dissolving in 5% aqueous sodium hydroxide. 

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