1:5 acid will be carried down with it). Both methods appear, however, to be of about the same value.

The 1:8-naphthylamine sulphonic acid or peri-acid is not used directly as such for the preparation of dyes, but is first converted into various other compounds. The most important of these are Naphtha-sultone, Phenyl-naphthylamine sulphonic acid 1:8 (Phenyl-peri-acid), and the Amino-naphthol sulphonic acids 1:8:4 and 1:8:2:4.

Their method of formation is shown in the following scheme: -

S-acid, or amino-naphthol sulphonic acid 1:8:4.

Amino-naphtholdisulphonic acid 1:8:2:4.

Chicago-acid, or SS-acid.

The naphthylamine sulphonic acid 1:8 may be converted into the diazo compound on treatment with nitrous acid (sodium nitrite) in mineral acid solution at 25°. On heating this in aqueous solution to 550 a quantitative yield is obtained of naphtha-sultone (I.). The yield of sultone obtained is a direct measure of the purity of the starting material; it is practically always converted into the naphtha-sultone sulphonic acid which, on coupling with azo components, yields dyes which are very pure and fast to light. During recent years, however, the importance of these colouring matters has diminished considerably.

Again, the naphthylamine sulphonic acid 1:8 may be converted into its arylated derivatives; thus the technically important phenyl-naphthylamine sulphonic acid 1:8 may be obtained by heating the free naphthylamine sulphonic acid with aniline (II.).

One part of the free sulphonic acid is heated with three times its weight of aniline (or p-toluidine) to 160o in an enamelled vessel, which is heated in an oil bath. The water, which is always present in the substance, is distilled off in vacuum, the product being afterwards heated for 24 hours with continuous stirring. The excess of aniline is carefully distilled off, the aniline salt of the resultant phenylated acid is then decomposed by means of the calculated quantity of soda-lye, and the residual aniline is driven off with steam, thus obtaining a solution of the phenyl-naphthylamine sulphonic acid, which is then coupled directly with diazotized H-acid in acetic acid solution. If the process has been correctly carried out, the acid itself need not be isolated. The resultant dye is Sulphon Acid Blue R (Bayer), which is fast to light.

If the naphthylamine sulphonic acid is sulphonated with oleum, the di- or tri-sulphonic acid is produced (or the anhydro compounds, the Naphthasultams) according to the strength. These two products are fused with caustic potash in an open pan at 200-210°, and yield the corresponding amino-naphthol sulphonic acids (III. and IV.). Both are intermediates for the production of wool and cotton colours.

Naphthylamine sulphonic acid 1:5 is of less importance, and can only be dealt with briefly. It is either diazotized and coupled with amines and naphthols, or is worked up into amino-naphthol sulphonic acid 1:5:7.

As indicated in the above scheme, the 1:5 acid differs from the 1:8 acid, in that it must be acetylated before sulphonation, as it is otherwise destroyed by the sulphuric anhydride. Acetylations of this kind play a not unimportant part in the technology of dyes (of. Amidonaphthol Red G).

Sulphonation of β-Naphthol

On sulphonating β-naphthol a considerable number of mono-and poly-sulphonic acids are obtained according to the concentration and the temperature of the sulphuric acid used. Only a few typical cases will be discussed, in order that the beginner may be able to arrive at an idea of this branch of manufacture of intermediate products.

As is well known, β-naphthol sulphonates chiefly in the 6-position on treatment with sulphuric acid of 66° Be. (93 %); that is to say, naphthol sulphonic acid 2:1 is first formed,. which is rapidly isomerized to the 2:6 acid (Scharffer acid).

Reaction:

If an excess of acid be used, a certain amount of the 2:3:6 and 2:6:8 acids are always formed as well which, owing to their property of combining with diazonium compounds to give respectively reddish or yellowish dyes, are usually known by the names of R-acid and G-acid.1

Formulae:

According to whether the sulphonation is warm or cold, relatively more R- or G-acid is formed respectively. All three of the acids in question are important intermediates for the production of azo colours. As it is absolutely impossible to obtain the three isomers by themselves, it becomes necessary to separate them very carefully from their mixture.

•It is important to emphasize the fact that the β-naphthol which is to be used must be powdered. If this elementary precaution be neglected, that portion of the naphthol which first enters into reaction becomes sulphonated at the expense of the coarse lumps, which swim about in the reaction mass, and it is impossible to obtain uniform results. This will also be the case if the reaction mixture be allowed to stand instead of being continuously stirred. The apparatus is the same as that for β-naphthalene sulphonic acid.

1 German: Rot = red; Gelb = yellow.

Naphthol Sulphonic Acid 2:6 and Disulphonic Acid 2:3:6

(Schaffer Acid and R-acid).

142 Gms. (1 mol.) of pure, finely powdered β-naphthol are added to 200 gms. of 100 % sulphuric acid with stirring. The temperature rises rapidly to about 8o°, at which it is left for about a quarter of an hour to ensure a homogeneous mixture. The temperature is then raised to 100-110o, stirring continuously, until a test portion no longer shows any separation of β-naphthol on pouring into water. This will occupy about 3 hours. The mixture is then poured into 1 litre of water, and is neutralized with about 200 gms. calcium carbonate. A warm solution of Glauber salt is now added to the pasty gypsum mixture. A clear, filtered test portion should not give any turbidity with Glauber salt. The whole is then filtered and the gypsum washed out. (For this purpose the factories make use of waste Glauber salt from the H-acid or other caustic soda melt, which they can obtain at less than 1 franc per 100 kgs.) The sodium salts are evaporated down in a porcelain dish over a bare flame to half a litre (a vacuum is used in the works) and the relatively sparingly soluble sodium-2:6-sulphonate salted out with sufficient common salt for the solution to contain 20 % of salt (in the present case 100 gms.). With good stirring the Schaffer salt separates out completely during the course of a day. It is filtered off and washed with a very little concentrated brine. The aqueous solution of the Schaffer salt purified in this manner should show only slight fluorescence. The filter cakes are well pressed in a screw-press and consist of very pure Schaffer salt, containing only a very little R-salt. The mother-liquor is acidified with concentrated sulphuric acid and allowed to stand for some time. In the laboratory, 10-12 hours will suffice, but on the large scale several days are required, before the acid sodium salt of R-acid has separated out completely. It is extremely easily soluble, so that in some circumstances the mother-liquor itself can be coupled directly with an azo component to a dye of the Ponceau series (e.g. with meta-xylidine to give Ponceau R).