2-tolidine

Make a thin paste of 21 5 g. of finely-powdered o-tolidine (a commercial product) with 300 ml. of water in a 1-litre beaker, add 25 g. (21 ml.) of concentrated hydrochloric acid, and warm until dissolved. Cool the solution to 10° with ice, stir mechanically, and add a further 25 g. (21 ml.) of concentrated hydrochloric acid (1) partial separation of o tolidine dihydrochloride will occur. Add a solution of 15 g, of sodium nitrite in 30 ml. of water as rapidly as possible, but keep the temperature below 15° a slight excess of nitrous acid is not harmful in this preparation. Add the clear, orange tetrazonium solution to 175 ml. of 30 per cent, hypophosphorous acid (2), and allow the mixture to stand, loosely stoppered, at room temperature for 16-18 hours. Transfer to a separatory funnel, and remove the upper red oily layer. Extract the aqueous layer with 50 ml, of benzene. Dry the combined upper layer and benzene extract with anhydrous magnesium sulphate, and remove the benzene by distillation (compare Fig. II, 13, 4) from a Widmer or similar flask (Figs. II, 24, 3-5) heat in an oil bath to 150° to ensure the removal of the last traces of benzene. Distil the residue at ca. 3 mm. pressure and a temperature of 155°. Collect the 3 3 -dimethyldiphenyl as a pale yellow liquid at 114-115°/3 mm. raise the bath temperature to about 170° when the temperature of the thermometer in the flask commences to fall. The yield is 14 g. 

If the hydrochloric acid is added all at once instead of in two portions as detailed, a solid will be obtained consisting of o-tolidine coated with its dihydrochloride, and the diazotisation will proceed slowly. 

Investigated is the influence of the purity degree and concentration of sulfuric acid used for samples dissolution, on the analysis precision. Chosen are optimum conditions of sample preparation for the analysis excluding loss of Ce(IV) due to its interaction with organic impurities-reducers present in sulfuric acid. The photometric technique for Ce(IV) 0.002 - 0.1 % determination in alkaline and rare-earth borates is worked out. The technique based on o-tolidine oxidation by Ce(IV). The relative standard deviation is 0.02-0.1. 

Z)-Tolidine (3,3 -dimethylbenzidine) [119-93-7] M 212.3, m 131-132", pK 4.45. Dissolved in benzene, percolated through a column of activated alumina and crystd from benzene/pet ether. 

Titanium diboride Titanium dioxide o-Tolidine based dyes Toluene... 

Spray solution 2 Solution of potassium iodide and p-tolidine in glacial acetic acid/water. 

Spray solution 3 Dissolve 1 g o-tolidine in 100 ml acetic acid (10%). 

Warning The substances benzidine and o-dianisidine, which are classified as carcinogenic, react in a similar manner to o-tolidine, which is also suspected of causing cancer. 

Note The TDM reagent can be used everywhere, where o-tolidine is employed. It can also be used on chromatograms, that have already been treated with ninhydrin, Pauly or ammonia perchlorate reagent or with iodine vapor [1]. Water may be used in place of 80% 2-propanol when making up solutions II, III and IV. The chlorine gas atmosphere in the chromatography chamber can also be created by pouring 5 ml hydrochloric acid (ca. 20%) onto 0.5 g potassium permanganate in a beaker such a chlorine chamber is ready for use after 2 min. 

Spray solution Dissolve 160 mg o-tolidine in 30 ml glacial acetic acid and make up to 500 ml with water dissolve 1 g potassium iodide in this solution [4, 14, 16, 17, 28-30]. 

Caution o-Tolidine is very toxic and possibly carcinogenic For this reason the dipping method should be preferred. This is the only way to ensure that the spray mist does not reach the respiratory tract or skin. 

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