Hydrosulfite Types - BASF

Technical Information 

Hydrosulfite Types 

TI/T 7015 e 

October 1997 (RB) 

Supersedes TI/T 1489 dated January 1993 

® = Registered trademark of 

BASF Aktiengesellschaft 

Hydrosulfite Conc. BASF 

Hydrosulfite Conc. BASF N 

Hydrosulfite F Conc. BASF 

Hydrosulfite FE Conc. BASF 

Reducing agents for the textile industry 

Textile and Leather Dyes and Chemicals

Nature 

Physical form 

Storage stability 

Anhydrous sodium dithionite (Na 2 

S 2 

O 4 

), technical grade, stabilized 

Powder 

Hydrosulfite Conc. BASF and Hydrosulfite Conc. BASF N have a shelf life 

of up to 24 months. 

Hydrosulfite F Conc. BASF and Hydrosulfite FE Conc. BASF have a shelf 

life of up to 12 months. 

Storage 

All Hydrosulfite types must be stored in closed containers, and the 

containers must be protected from moisture. 

If the products are not stored under suitable conditions or if moist scoops 

are used to take product out of the containers, or if moisture enters a containers, 

the product decomposes. The moist product becomes lumpy and 

it develops heat and gases (with the odour of sulphur dioxide), resulting 

finally in spontaneous combustion, particularly in the presence of atmospheric 

oxygen (cf. “Action in the case of spontaneous combustion” on 

page 7). 

Handling of partially 

decomposed product 

Impurities 

Hydrosulfite that has become lumpy must immediately be removed from 

the drum by passing it through a coarse sieve, after which the lumps must 

be dissolved in water. Only the residual, powdery product is fit for use. 

BASF’s Hydrosulfite types are practically free of heavy metals (below the 

level of detectability). 

2

Properties 

Physical and chemical data 

Appearance 

Solubility 

White powder 

Readily soluble in dilute alkalis: approx. 250 g/l at 20 °C. The solution is 

water-white without any turbidity. 

,,, 

500 

,,, 

400 

,,, 

300 

,,, 

dissolved 

undissolved 

,,, 

200 

,,, 

100 

,,, 

,,, 

0 

0 100 200 300 400 

Hydrosulfite Conc. BASF (g/l) 

Caustic soda 38 °Bé (ml/l) 

Fig. 1 

Solubility of Hydrosulfite Conc. BASF in the presence of alkali 

Stability of the solutions 

Hydrosulfite solutions have a strong reducing action and bind atmospheric 

oxygen. 1 m 3 of air binds roughly 1.7 kg of hydrosulfite. Hydrosulfite reacts 

with atmospheric oxygen many times more rapidly than its own relatively 

slow decomposition. In working with dissolved hydrosulfite, contact with 

air must therefore be avoided as far as possible. In acid media, hydrosulfite 

decomposes to form mainly sulphur dioxide, sulphur and other 

sulphur-containing compounds. Alkalis have a stabilizing action on 

solutions of hydrosulfite, particularly when the solution is exposed to air. 

3

Hydrosulfite Conc. BASF (g/l) 

30 

20 

exclusion of air 

presence of air 

without alkali 

10 

50 ml/l NaOH 38 °Bé 

30 g/l Hydrosulfite Conc. BASF 

25 °C 

0 

0 2 4 6 8 10 

h 

Fig. 2 

Stability of hydrosulfite solutions under various conditions 

pH value 

Hydrosulfite Conc. BASF and 

(50 g/l in water) Hydrosulfite Conc. BASF N 7– 9 

Hydrosulfite F Conc. BASF and 

Hydrosulfite FE Conc. BASF 6 – 7 

For pH measurements, oxygen must be completely excluded. The 

measurement must be carried out under nitrogen and with air-free water. 

Bulk density 

The Hydrosulfite types vary in their bulk density. This must be taken into 

consideration in volumetric metering. 

Hydrosulfite Conc. BASF 1300 –1400 g/dm 3 

Hydrosulfite Conc. BASF N 1150 –1250 g/dm 3 

Hydrosulfite F Conc. BASF and 

Hydrosulfite FE Conc. BASF 750 – 900 g/dm 3 

Action 

Preparation of 

hydrosulfite solutions 

In the textile industry, hydrosulfite is used mainly as a reducing agent for 

vat dyes and for the reductive clearing of dyeings on polyester. It is also 

suitable for stripping dyeings and for cleaning dye becks, dyeing 

machines, etc. 

Hydrosulfite solutions are best prepared immediately before use. The alkali 

should be added to the bath first, after which the hydrosulfite powder is 

strewed into the bath with stirring. 

The process can be carried out very economically by using a dissolving 

station and obtaining the product in containers. 

This method has the following advantages: 

– no dusting 

– less risk of fire 

– lower product wastage 

4

In this method, a solution is prepared containing approx. 130 g/l of hydrosulfite 

together with the requisite amount of alkali (260 ml/l of NaOH 

38 °Bé). The solution is then piped to the department where it is required. 

This concentrated reducing agent solution only has to be diluted and is 

then ready for use. 

Applications 

As a reducing agent for vat dyes 

The main field of application for hydrosulfite is the reduction of vat dyes in 

order to convert them into a water-soluble form with affinity for the fibre. 

The vat dyes are either reduced direct in the dyebath or, as in pigmentation 

dyeing processes, pigment padding processes, and two-phase printing, 

they are first applied to the textile material in an insoluble form and 

then subsequently developed with hydrosulfite and caustic soda. 

The reducing action of hydrosulfite depends on the temperature and the 

pH. Under the conditions of an IN vat, the redox potential is approx. 

–1000 mV. This potential is sufficient to convert all commercially available 

vat dyes into the water-soluble sodium leuco compound, because all of 

these dyes are reduced in the potential range of approx. – 650 to – 950 mV. 

The dye must remain completely vatted throughout the whole dyeing process. 

However, since the hydrosulfite is continuously decomposed by the 

action of air, with consumption of alkali, the vat must always contain an 

excess of hydrosulfite and caustic soda. 

The presence of this excess must be ensured throughout the entire 

dyeing process. The simplest method is to check the alkalinity with 

phenolphthalein paper, and the reducing action with Vat Yellow paper. 

The amounts of hydrosulfite necessary for the various dyeing processes 

are indicated in our pattern card for Indanthren ® dyes, MK/T 266. 

For the reductive clearing of dyeings 

Dyeings and prints produced with disperse dyes on polyester fibres, 

triacetate fibres, and various fibre blends are cleared with alkaline 

hydrosulfite solutions in order to obtain the best possible standard of 

fastness. 

4– 8 ml/l caustic soda 38 °Bé 

2– 3 g/l Hydrosulfite Conc. BASF 

0.5 g/l Uniperol ® EL 

20 min at 70 – 80 °C 

Vat dyes Liquor ratio 10 :1 to 30 :1 

For stripping or partial stripping of dyeings and prints 

Hydrosulfite is suitable for the reductive stripping of dyeings and prints 

produced with vat, direct, and reactive dyes on cellulosic fibres. 

In package systems 

and winches 

Set the bath at 75 – 80 °C with 

0.5 g/l Dekol ® S 

2– 3 g/l Setamol ® WS 

10– 15.5 ml/l caustic soda 38 °Bé 


1 g/l glucose 

(for vat dyes that are sensitive to over-reduction) 

2– 3 ml/l Albigen ® A 

and treat the textile material for 3 min at 75 – 80 °C (with indirect steam). 

Ensure that a fully vatted state is maintained. 

5

Rinse with 

1 ml/l caustic soda 38 °Bé 


1 g/l Setamol WS 

for 5 min at room temperature, and then rinse with cold water with 

overflow. If necessary, then oxidize at 55 °C with 

1– 2 ml/l hydrogen peroxide 35%. 

On the jig 

Liquor ratio 5 :1 for pale shades and up to 10 :1 for dark shades 

Set the bath at 75 – 80 °C with 

1 g/l Dekol S 

3– 5 g/l Setamol WS 

20 ml/l caustic soda 38 °Bé 


1 g/l glucose 

(for dyes that are sensitive to over-reduction) 

2– 3 g/l Albigen A 

and treat the dyeing over 4 ends, but never longer than for 40 min at 

75 – 80 °C (with indirect steam). Ensure that a fully vatted state is 

maintained. 

As the dye-Albigen A addition compounds have low solubility (with formation 

of tarry deposits under certain conditions), short liquor ratios and long 

treating times must be avoided. If necessary, the stripping process should 

be repeated. The goods are then rinsed with cold water with overflow, and 

than oxidized with 1– 2 ml/l of hydrogen peroxide 35% at 55 °C. 

Direct dyes 1.5 g/l soda ash 


2 g/l Albigen A 

30 – 60 min at 50 °C 

followed by intensive rinsing. 

Reactive dyes 15 ml/l caustic soda 38 °Bé 

5 ml/l Hydrosulfite Conc. BASF 

2 ml/l Albigen A 

30 – 60 min at 60 – 80 °C 

followed by intensive rinsing. 

For cleaning dyeing machines and equipment 

Alkaline solutions of hydrosulfite are used to remove dye residues from 

dyeing machines, mixing vessels, rollers, etc. The cleaning action of the 

solutions can be promoted by adding Albigen A or Uniperol AC. 

Safety 

When using this product, the information and advice given in our Safety 

Data Sheet should be observed. Due attention should also be given to 

the precautions necessary for handling chemicals. 

Contact of the products with oxidizing agents (hydrogen peroxide, sodium 

chlorite, and sodium hypochlorite) must be avoided under all conditions. 

Hydrosulfite must always be kept at a safe distance away from these 

agents. 

Action in the case of spontaneous combustion 

See our Technical Information Bulletin TI/T 311 e of July 1997: 

Measures to be taken in the case of fire or accidents in transportation. 

6

Note 

The information submitted in this publication is based on our current 

knowledge and experience. In view of the many factors that may affect 

processing and application, these data do not relieve processors of the 

responsibility of carrying out their own tests and experiments; neither do 

they imply any legally binding assurance of certain properties or of suitability 

for a specific purpose. It is the responsibility of those to whom we 

supply our products to ensure that any proprietary rights and existing laws 

and legislation are observed. 

7

Printed in Germany 

Regional Marketing 

Asia 


North America, Canada 

and Mexico 


South America 


Europe, Africa and West Asia 

BASF Textile and Leather 

Dyes and Chemicals Pte. Ltd. 

7 Temasek Boulevard 

#35-01 Suntec Tower One 

Singapore 038987 

Tel.: (65) 432 34 00 

Fax.: (65) 432 34 34 

BASF Corporation 

Textile /Leather Colors and 

Chemicals 

4330 Chesapeake Drive 

Charlotte, NC 28216, USA 

Tel.: (1) 704 398 43 80 

Fax.: (1) 704 398 42 50 

BASF S.A. 

Química Têxtil 

Estrada Samuel Aizemberg 1707 

09851-550 São Bernardo do Campo/ 

São Paulo - Brazil 

Tel.: (55) 11 751 22 33 

Fax.: (55) 11 751 69 89 

BASF Aktiengesellschaft 

Textil- und Lederchemie 

67056 Ludwigshafen/Germany 

Tel.: (49) 621 60 41366 

Tel.: (49) 621 60-0 

Fax.: (49) 621 60 78452 

Telex: 46499-0 bas d 

Textile and Leather Dyes and Chemicals

Hydrosulfite Types - BASF

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