Sodium—continued weighing

Vinylacetic acid. Place 134 g. (161 ml.) of allyl cyanide (3) and 200 ml. of concentrated hydrochloric acid in a 1-htre round-bottomed flask attached to a reflux condenser. Warm the mixture cautiously with a small flame and shake from time to time. After 7-10 minutes, a vigorous reaction sets in and the mixture refluxes remove the flame and cool the flask, if necessary, in cold water. Ammonium chloride crystallises out. When the reaction subsides, reflux the mixture for 15 minutes. Then add 200 ml. of water, cool and separate the upper layer of acid. Extract the aqueous layer with three 100 ml. portions of ether. Combine the acid and the ether extracts, and remove the ether under atmospheric pressure in a 250 ml. Claisen flask with fractionating side arm (compare Fig. II, 13, 4) continue the heating on a water bath until the temperature of the vapour reaches 70°. Allow the apparatus to cool and distil under diminished pressure (compare Fig. II, 20, 1) , collect the fraction (a) distilling up to 71°/14 mm. and (6) at 72-74°/14 mm. (chiefly at 72 5°/ 14 mm.). A dark residue (about 10 ml.) and some white sohd ( crotonio acid) remains in the flask. Fraction (6) weighs 100 g. and is analytically pure vinylacetic acid. Fraction (a) weighs about 50 g. and separates into two layers remove the water layer, dry with anhydrous sodium sulphate and distil from a 50 ml. Claisen flask with fractionating side arm a further 15 g. of reasonably pure acid, b.p. 69-70°/12 mm., is obtained. 

Notes. (1) For elementary students, it is sufficient to weigh out accurately about 1.7 g of sodium oxalate, transfer it to a 250 mL graduated flask, and make up to the mark. Shake well, Use 25 mL of this solution per titration and add 150mL of ca 1M sulphuric acid. Carry out the titration rapidly at the ordinary temperature until the first pink colour appears throughout the solution, and allow to stand until the solution is colourless. Warm the solution to 50-60 °C and continue the titration to a permanent faint pink colour. It must be remembered that oxalate solutions attack glass, so that the solution should not be stored more than a few days. 

To 3600 g. of concentrated sulfuric acid, in a 5-I. flask placed in an empty water bath, are added 360 g. of technical trinitrotoluene, while the mixture is stirred mechanically. Sodium dichromate (Na2Cr207 2 H20) is now added in small quantities (precaution see Notes), with constant stirring, until the temperature of j he mixture reaches 40° the empty water bath i now filled with cold water and the addition of sodium dichromate continued at such a rate that the temperature remains at 45-55°. In all 540 g. of sodium dichromate are added, the addition taking one to two hours. When all has been added, the mixture, which has now become very thick, is stirred for two hours at 45-55°, and poured into a crock containing 4 kg. of crushed ice. The insoluble trinitrobenzoic acid is filtered off, and carefully washed with cold water until free from chromium salts. On drying it weighs 320-340 g. 

Procedure Weigh accurately about 0.5 g of ferric ammonium citrate and dissolve the sample in 15 ml DW. Add to it slowly 1 ml of sulphuric acid and warm gently to attain a yellow colouration so as to decompose the iron and ammonium citrate complex completely. Cool and add 0.1 N potassium permanganate solution dropwise from a burette to obtain a pink colour that persists for 5 seconds. To the resulting solution add hydrochloric acid 15 ml and potassium iodide 2.0 g, shake well and set aside for 3 minutes so that iodine may be liberated completely. Now, add 60 ml of water and titrate with 0.1 N sodium thiosulphate solution while shaking the contents continuously till a colourless end-point is achieved. 

Procedure Weigh accurately about 0.15 g of calcium chloride dihydrate and dissolve it in 50 ml of DW. Titrate with 0.05 M disodium ethylenediamine tetracetate to within a few ml of the expected end point, add 8.0 ml of sodium hydroxide solution and 0.1 g of calcon mixture and continue the titration until the colour of the solution changes from pink to a full blue colour. Each ml of 0.05 M disodium ethylene disodium tetracetate is equivalent to 0.007351 g of CaCl2.2H20. 

Procedure Weigh accurately about 0.5 g of phthalylsulphathiazole and heat on a water-bath for 2 hours after the addition of 10.0 ml of sodium hydroxide solution. Cool the contents of the flask to 15°C in an ice-bath, add to it 10.0 ml of water and 20.0 ml of hydrochloric acid and carry out the titration slowly with 0.1 M sodium nitrite solution. The contents of the flask are shaken thoroughly and continuously until a distinctly visible blue colour is obtained when a drop of the titrated solution is placed on a starch-iodide paper 5 minutes after the last addition of the 0.1 M NaN02 solution. Towards the approach of the endpoint the addition of NaN02 solution must be at the rate of 0.1 ml. Each ml of 0.1 M sodium nitrite is equivalent to 0.04034 g of C17H13N305S2. 

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