|In this paper it has been decided to refrain from a purely technical discussion and to treat the subject of the manufacture of sulphur dyes in
a general and rather practical matter. Sulphur dyes have been generally regarded and for the purpose of this paper will be considered as
those dyes which are applied to the fiber by the aid of the alkaline sulphides, the most common, and, in fact, the sulphide of universal use
being the well- known sodium sulphide of commerce.
The means of manufacturing sulphur dyes were discovered late in the ‘90’s, and this class of dyes first found general and favorable use
from 1900 to 1910, after overcoming much prejudice which many present will easily recall.
For the sake of clarity the manufacture of sulphur dyes has been divided into two main subdivisions. First, that class of sulphur dyes that
are manufactured by the baking, roasting or so-called dry fusion process. A few examples of this class are the Sulphur Browns, Sulphur
Tans and Crutches and Sulphur Yellows of the redder shades. And second, that class manufactured by the so-called wet fusion process, a
few typical examples of which are Sulphur Blacks, Sulphur Navy, Sky, and Brilliant Blues, Sulphur Bordeaux and Sulphur Green. In general,
subject to certain exceptions, the cheaper and duller dyes are made by the dry fusion process, some of which, however, have exceptional
fastness and good working qualities, and the brighter more expensive shades are produced by the wet or aqueous fusion process.
One typical shade or type has been selected from each of these general classes for rather detailed study. From the dry process class
Sulphur Yellow of the soluble reddish type largely used in combination for producing khaki shades has been selected, and from the wet
fusion class the well-known Sulphur Navy Blue has been selected as typical.
An outline of the process for manufacturing Sulphur Yellow of the reddish type is as follows:
Certain definite amounts of sulphur, meta-toluene-dyamine or the formyl, diformyl and aldehyde derivatives of meta-toluene-dyamine and
benzidine are heated in an iron pot, kettle or mixer to about 300 deg. Cent. or 575 deg. Fahr. for a period of time about 12 to 30 hours.
During this process hydrogen sulphide is evolved and towards end of the reaction the mass becomes quite thick. At this point in the
process the semi-fluid mass is sometimes transferred to pans, and the process carried to completion by continued heating at higher
temperatures in a so-called baking oven, constructed in general along the lines of a bakery oven in an ordinary kitchen range or a
commercial bakery. The baking process is usually carried on with the exclusion of air to prevent combustion of the dyestuff, until the
mass becomes quite stiff. When the reaction is considered complete the furnace is allowed to cool, whereupon the mass becomes quite
hard and brittle.
Formerly quite a number of tans and browns were taken at this point and merely ground to the desired fineness, blended with salt for
standardization and marketed in the crude state. Even now some of the cheaper dark browns and tans are found on the market prepared
in this way. However, the best practice is to insure a uniform product with the minimum of insoluble matter is to dissolve this mass in a
solution of sodium sulphide or caustic soda, filter the solution and precipitate the refined dyestuff from the solution by the use of an acid
and acid salt or by blowing air through the dilute solution to oxidize the sulphide. The liquor containing the dyestuff in suspension is then
filtered, the precipitated dyestuff dyed, ground, blended with salt, sodium sulphate, etc., to standardize, and marketed.
We will now take up in a general way the manufacture of Sulphur Navy Blue as representative of the wet fusion process class.
The first step in this process is the preparation of para-nitroso phenol, which is formed by the action of sodium nitrite on phenol (carbolic
acid) in an acid solution at a temperature of near 0 deg. Cent. This para-nitroso phenol is filtered, wrung in an extractor, analyzed and
stored in a cool place. It is quite combustible and inflammable, and great care must be used in handling and storing it.
The second step is the preparation of the color base or the indo-phenol by the condensation at low temperatures in a solution of sulphuric
acid of the para-nitroso phenol and ortho-toluidine. When this extremely delicate reaction is complete, the mass is run into a dilute solution
of soda ash and the acid neutralized with the resultant precipitation of the indo-phenol which is filtered and analyzed but not dyed, as the
color base is quite unstable and must be used fresh.
The third step is the preparation of a sodium polysulphide by heating together certain quantities of sodium sulphide in solution and sulphur.
The indo-phenol is then dissolved in the sodium polysulphide, the solution brought to a definite boiling point by evaporation or dilution and
run at boiling in a closed tank or kettle equipped with a reflux condenser for a certain period from 12 to 100 hours until reaction is
completed. During the fusion cycle there is quite an evolution of hydrogen sulphide. The strength of the polysulphide, the proportion of
sulphur to the sulphide, the temperature and the time of the fusion reaction are all varied to produce the desired shades. Also certain
solvents and fusion assistants are sometimes employed to produce certain shade or solubility results. Among these assistants are
alcohol, glycerine and their derivatives.
The fourth step consists of diluting the completed fusion and precipitating the dyestuff from the sulphide solution by means of acid, acid
salts, or by blowing air through the solution to oxidize the sulphide.
The fifth step consists of filtering the precipitated dyestuff drying, grinding, aging and standardizing by blending various batches and
reducing with salt, sodium sulphate, etc., and marketing.
It is quite essential in almost all classes of sulphur dyes to give them an aging process after the finished dyestuff is dried. This is to permit
the dyestuff to take up from the atmosphere the desired amount of moisture and oxygen to become more stable in this respect; otherwise
the change goes on after standardization, resulting in an “off standard” dye, and is some cases when the barrel is opened and the dyestuff
permitted to come in contact with the air a rapid oxidation takes place with the resulting firing of the dyestuff in the barrel.
The kind of water used in the various manufacturing processes also exerts a powerful influence on the shade and solubility of the dye. In
general, the purer the water the more soluble and brighter the dye. Soluble metallic salts in the water exert a very harmful influence.
Lead, iron and wood are the principal materials of which the apparatus is constructed. Iron is nearly always preferable owing to its low
cost and permanency where its use is permitted. Some dyes are very sensitive to iron, in which cases it is necessary to resort to other
metals. Certain sulphur dyes that are sensitive to iron can be produced in lead apparatus, and when dyed in glass or porcelain dye pots in
the laboratory give brighter shades. However, when dyed in iron machines the shade is materially affected so that most of the apparent
advantage of the lead apparatus is lost. Others are not so sensitive to iron in dyeing and lead or lead lined apparatus is quite desirable.
Copper or brass must be avoided around the sulphide fusion kettles, as the copper is readily affected by the sulphide. Also wrought iron
and steel are more resistant to sulphide than cast iron.
The most desirable location for a factory to make high grade sulphur dyes is:
1) Where an abundance of pure water is available.
2) Where sewage disposal can be readily affected and where obnoxious fumes are not prohibited.
3) Where high grade intelligent labor is available.
4) Where the source of raw material is near and where the market for the product is sufficiently close to avoid too much delay in shipping
the product. The amount of raw materials used exclusive of fuel is often about 8 to 10 times the weight of the finished dyestuff. Therefore,
the proximity of the factory to the source of supply of the chemicals is more important from the standpoint of transportation than to be
close to the consumer. However, the question of service to the consumer must have serious consideration.
5) Where power or fuel or both are cheap.
6) Where the climate is not too rigorous to prohibit the use of lightly constructed buildings, as light and ventilation are prime essentials.
We have covered a general outline of two typical processes of the two general classes of sulphur dyestuffs, also some generally related
factors. Now from the time the process for the first intermediate is begun until the dyestuff is in the barrels in a dry warehouse the factors
of proportions of the various chemical ingredients, the factors of time, temperature, concentration, agitation and other plant conditions
must be controlled within very narrow and predetermined limits. All these factors have a direct bearing on the properties of the dyestuff,
such as shade, strength, solubility, uniformity, fastness, property of changing much or little on oxidizing and after-treating, and, in fact,
practically all the properties of the dyestuff are subject to and controllable by the various factors above mentioned. During all these
processes accurate laboratory control must be maintained as a check on and a guide to the plant procedure. This includes analyses of
raw materials and intermediates and a constant checking of finished batches regarding all their properties.
Of all the classes of dyestuffs, the sulphur dyes, because they are in most cases not definite chemical individuals but mixtures of many,
are most susceptible to plant factors and conditions, and consequently they require the greatest amount of care in their preparation. It
might be said that the single greatest factor contributing to the manufacture of a high-grade sulphur dye is eternal vigilance all the way
down the line.
It is difficult to pass from the subject of manufacturing without touching on the testing of the dyestuff in the laboratory of the producer, and
likewise in the laboratory of the dealer or sales agent and the consumer. Almost all sulphur dyes are undetermined and undeterminable
mixtures of various related chemical individuals, and very few are definite chemicals themselves. Also the properties of fastness and
solubility, properties of being reduced and oxidized, properties in respect to aftertreating and exhaustibility are all strictly relative
properties. Therefore, with so many variables it is essential that the producer, the agent and the consumer all follow the same testing
procedure to the minutest detail if comparable results are to be expected. The producer should know the use to which his product is to be
put, and all parties concerned should adjust their dyeing and testing procedure to the closest approximation of the consumers’ conditions
as is possible to do so.
It is of greatest importance to the manufacturer and also of great mutual benefit to the consumer when the manufacturer can know to
what use his product is to be put by the consumer. Only in this way can the best results be secured by both, for the manufacturer, knowing
certain mill conditions, can often change his processes so as to give to a certain color certain qualities that are especially desirable under
given mill conditions, whereas, had he not known these peculiar conditions, his product, while suitable for most conditions, might be
unsuited to this particular condition. In this event neither the manufacturer nor his product nor the consumer nor his conditions are to be
wholly blamed; ignorance and unwillingness to co-operate are the causes of most troubles along this line.
The manufacturers observe with unmixed gratification the constantly improved personnel in the dyehouses, and he looks forward to the
time when all dyehouse superintendents will be technical experts trained in the application of dyes and related subjects.
May we all-manufacturers, dealers, agents, dyers and consumers-work and pray to the end that the time will soon come (and let us do our
part to hasten it) when there will exist a complete spirit of co-operation and helpfulness between consumer and manufacturer, and a
mutual willingness and desire to go to the bottom of our mutual troubles before blaming some product or condition, when in most cases
our troubles can be eliminated or minimized by intelligent co-operation.
*A paper read before the joint meeting of the South Central and Piedmont Sections of the American Association of Textile Chemists and
Colorists at Asheville, N.C., July 16, 1927.
|The Manufacture of Sulphur Dyestuffs*
By John L. Crist
Manager, Beaver Chemical Corporation, Damascus, Va.