Part 2

The amido acid forms a compound with tin which crystallizes from the HCl together with stannous chloride. This compound may be broken up and the tin removed by continued boiling with water.

A better method of removing the tin is by dissolving the compound in Na{2}CO{3}. This forms a salt with the amido acid and throws down the tin as Sn(OH)_{2}, a white flocculent precipitate. On filtering and adding to the solution conc. HCl, the free amido acid is deposited in characteristic colorless, rhombic crystals, having the formula

┌─ │CH{3} C{6}H{3}┤SO{2}OH (o) │NH_{2} (p) └─

The method at first employed for preparing the hydrazine compound consisted in treating the amido acid, suspended in HCl, with potassium nitrite and then with stannous chloride. The tin was then removed from the solution by the addition of sodium carbonate and the hydrazine compound thrown down with HCl. This method however gave poor results the yield being only about 50% of the theoretical.

Another method was accordingly substituted for the above, namely that of Strecker and Römer (Ber. IV. s 784.) By this the diazo compound is made first and isolated. This is done by suspending the finely powdered acid in absolute alcohol, cooling and passing a current of the oxides of nitrogen through in the ordinary way. The acid changes in appearance, becoming more crystalline and slightly darker and settles quickly on being shaken. The reaction here may be expressed thus--

┌─ ┌─ │ CH{3} │ CH{3} C{6}H{3} ┤ SO{2}OH + HNO{2} = C{6}H{3} ┤ SO{3} + 2H{2}O │ NH_{2} │ \ └─ │ N=N └─

When the reaction is completed as shown by the appearance of the suspended powder it is filtered and while still fresh is added to a solution of acid sodium sulphite as long as it continues to dissolve readily.

To this solution there is added a quantity of solution of acid sodium sulphite equivalent to that already used and the solution is then boiled. It has at first a deep red color but in a few moments becomes light reddish yellow. The reaction of HNaSO_{3} on the diazo compound may be represented in two stages, the first portion forming an addition product and the second acting as a reducing agent. Thus,

┌─ ┌─ │ CH{3} │ CH{3} 1. C{6}H{3} ┤ SO{3} + HNaSO{3} = C{6}H{3}┤ SO{2}ONa │ \ │ │ N═N │ N═NSO{3}H └─ └─ ┌─ │ CH{3} 2. C{6}H{3} ┤ SO{2}ONa + HNaSO{3} + H{2}O │ N═NSO{3}H └─ ┌─ │ CH{3} = C{6}H{3} ┤ SO{2}ONa + HNaSO{4}. │ NH-NHSO_{3}H └─

To the hot solution an excess of conc. HCl is added when the hydrazine compound separates in a few moments in lustrous yellow scales which completely fill the solution. On the addition of the HCl a large amount of SO{2} is given off from the excess of HNaSO{3} and the solution becomes deep red. When the hydrazine has separated the mother liquor is again yellow.

The reaction is represented as follows:

┌─ │CH{3} C{6}H{6}┤SO{2}ONa + HCl + H{2}O │NH-NHSO{3}H └─ ┌─ │CH{3} = C{6}H{3}┤SO{2}OH + H{2}SO{4} + NaCl │NH-NH_{2} └─

The yield of hydrazine when both the diazo and the NaHSO_{3} are freshly prepared is practically quantitative.

The hydrazine thus prepared was treated with a hot 10% solution of copper sulphate till a permanent blue color was obtained in the solution. Nitrogen is evolved and the copper sulphate is reduced to cuprous oxide which is precipitated as a red powder. The reaction is as follows.

┌─ │CH{3} C{6}H{3}┤SO{2}OH + 2CuSO{4} + H{2}O │NH-NH{2} └─ ┌─ = C{6}H{4}┤CH{3} + Cu{2}O + N{2} + 2H{2}SO{4} │SO_{2}OH └─

Chalk was added to the solution to precipitate the H{2}SO{4} and form a calcium salt of toluene-o-sulphonic acid. From this the sodium salt was made by adding a slight excess of Na{2}SO{3} and evaporating to dryness. The salt is very soluble being deliquescent in the air while the corresponding potassium salt is not. From 1538 gr. of para-nitro-toluene, 655 gr. of toluene ortho-sodium sulphonate were obtained.

Having thus obtained the toluene ortho-sulphonic acid the next step in the problem was to find a convenient method for converting this into ortho-sulph-benzoic acid. Two ways present themselves for accomplishing this end. (1) direct oxidation of this salt and (2) conversion into benzoic sulphinide from which the acid may be obtained. Both of these methods were tried.

Oxidation of toluene-o-sodium sulphonate.

┌─ C{6}H{4}─┤CH{3} │SO{2}ONa └─

The sodium salt of toluene-o-sulphonic acid is oxidized to ortho-sulphobenzoic acid with considerable difficulty by KMnO_{4} in neutral solution.

Thus two experiments showed that the oxidation was not complete after 24 hours boiling with excess of permanganate. If the solution be made alkaline however, the oxidation is completed in a few hours, yet the greatest difficulty still remains in the separation of the free acid from the products of oxidation in the solution. If HCl be added to the solution the acid salt

COOH ╱ C{6}H{4} ╲ SO_{2}OK

is formed and this has nearly the same solubility as the KCl also present. A better method therefore is to add a slight excess of H{2}SO{4} and evaporate nearly to dryness. In this way are formed sulphates and the free acid presumably. The mixture is heated with alcohol (95%) which extracts the acid leaving the greater part of the manganese salts. This extract is evaporated and reextracted with alcohol. To this solution BaCO{3} is added to precipitate the H{2}SO{4} and form the Barium salt of the o-sulphobenzoic acid. The solution is filtered from the BaSO{4} and just enough H{2}SO{4} is added to exactly precipitate the barium. The solution should thus contain only the free acid sought, which crystallizes out on evaporating to a small volume. While the method is theoretically possible it presents so many difficulties that it is practically useless. The yield is extremely small; only enough acid being obtained in this way to show that it was possible.

Formation of Sulphinide from toluene-o-sodium sulphonate.

The second method for obtaining free o-sulphobenzoic acid from toluene-ortho-sulphonic acid is by the conversion of the latter first into benzoic sulphinide and then into the free acid. The sulphinide was made essentially as described by Remsen (Am. Ch. Jour. Vol. I. p. 428) with a few changes in the details as follows.

┌─ The salt C{6}H{4}┤CH{3} finely pulverized and in portions │SO{2}ONa └─

of from 10 to 50 gr. was placed in a Florence flask; an equivalent quantity of PCl_{5} added; An inverted condenser was then attached and the flask shaken. The action takes place at once and involves sufficient heat to distill off the oxychloride formed in the reaction. This being returned to the flask by the condenser furnishes a liquid medium in which the reaction takes place more readily and completely than when it is not present. It is best to cool the flask at first and afterwards heat gently on the water bath. The reaction which takes place may be represented as follows.

┌─ ┌─ │CH{3} │CH{3} C{6}H{4}┤SO{2}ONa + PCl{5} = C{6}H{4}┤SO{2}Cl + POCl{3} + NaCl. └─ └─