Condensates of bis-(4-hydroxyphenyl) sulfone as tanning assistants, their preparation and use in the tanning of leather

A condensate of bis-(4-hydroxyphenyl) sulfone, an aldehyde, a dialdehyde and/or glyoxylic acid and aminoacetic acid or an N-substituted aminoacetic acid is prepared and used as a tanning assistant, in a process for tanning leather in combination with, in particular, aluminum tanning agents.

The present invention relates to a condensate of bis-(4-hydroxyphenyl) 
sulfone, an aldehyde, a dialdehyde and/or glyoxylic acid and aminoacetic 
acid or an N-substituted aminoacetic acid as a tanning assistant, its 
preparation and use and a process for tanning leather using this 
condensate in combination with, in particular, aluminum tanning agents. 
Chrome tanning is one of the most important tanning methods. However, there 
is increasing interest in chromium-free mineral tanning processes, for 
example because of the problem of eliminating chromium-containing 
wastewater or chromium-containing shavings. Instead of chromium compounds, 
other possibilities are, for example, aluminum, titanium or zirconium 
salts. However, particularly where aluminum compounds are used alone, the 
resulting leather has insufficient shrinkage temperatures. As a rule, 
shrinkage temperatures of 90.degree. C., preferably 100.degree. C., are 
desirable. Another disadvantage is that aluminum tanning agents are 
generally relatively easily washed out, ie. the leather has limited water 
resistance. 
J. Amer. Leather Chem. Assoc. 76 (1981), 230-244 describes the combination 
of mimosa extract with aluminum compounds as an alternative to chrome 
tanning. The disadvantage of this tanning process is the brown coloration 
of the leather due to the mimosa extract and insufficient lightfastness of 
the tanned leather. 
Condensates of phenols with formaldehyde and other aldehydes and amino 
compounds, such as amino acids, have long been familiar to the skilled 
worker. This type of reaction is disclosed in, for example, German Pat. 
No. 89,979 or V. J. Temkina et al., Z. Org. Chim. 7 (1971), 327. 
Condensates of bis-(4-hydroxyphenyl) sulfone with aldehydes and 
aminoacetic acid or an N-substituted aminoacetic acid were unknown to date 
or have not been used as tanning agents. 
It is an object of the present invention to provide a tanning agent or a 
tanning assistant for a chromium-free tanning process, where the 
disadvantages of insufficient lightfastness and brown coloration of the 
mimosa/aluminum tanning are avoided. 
We have found that this object is achieved by a condensate obtainable by 
reacting bis-(4-hydroxyphenyl) sulfone with a saturated aliphatic 
monoaldehyde of 1 to 4 carbon atoms or a dialdehyde of the formula 
EQU OHC--(CH.sub.2).sub.n --CHO 
where n is an integer from 0 to 4, and/or with glyoxylic acid, if necessary 
in the form of an alkali metal salt, and with an unsubstituted aminoacetic 
acid or N-substituted, if necessary in the form of an alkali metal salt or 
ammonium salt, in a molar ratio of bis-(4-hydroxyphenyl) sulfone to 
aldehyde, dialdehyde and/or glyoxylic acid or its alkali metal salt to 
unsubstituted or substituted aminoacetic acid or one of its salts of 
1:0.5-4:0.3 -4, the molar amount of aminoacetic acid or its derivative 
being less than or equal to the molar amount of aldehyde, dialdehyde 
and/or glyoxylic acid, in aqueous or aqueous alcoholic solution, as a 
tanning assistant, its preparation, the use of this tanning assistant 
together with chromium-free mineral tanning agents, and a process for 
tanning leather in combination with, in particular, aluminum tanning 
agents. 
The preferred molar ratios of bis-(4-hydroxyphenyl) sulfone to aldehyde, 
dialdehyde and/or glyoxylic acid to unsubstituted to substituted 
aminoacetic acid or its salt are 1:0.8-2.5:0.5-2. 
The particularly noteworthy condensates are obtained from 
bis-(4-hydroxyphenyl) sulfone, formaldehyde or glyoxal and iminodiacetic 
acid or its alkali metal or ammonium salts. 
The novel tanning process leads to a leather having high shrinkage 
temperatures of 90.degree.-96.degree. C. Compared with the known brown 
leather obtained in mimosa/ aluminum tanning, the colour of the leather is 
ivory to white. The leather has very good lightfastness. Another advantage 
is that the pale natural colour remains unchanged even on prolonged 
storage at elevated temperatures of, for example, 60.degree.-80.degree. C. 
The novel condensates are obtained by reacting bis-(4-hydroxyphenyl) 
sulfone with a saturated aliphatic monoaldehyde of 1 to 4 carbon atoms, a 
dialdehyde of the formula 
EQU OHC--(CH.sub.2).sub.n --CHO 
where n is an integer from 0 to 4, or glyoxylic acid, if necessary in the 
form of an alkali metal salt, and unsubstituted or N-substituted 
aminoacetic acid, if necessary in the form of an alkali metal or ammonium 
salt, in molar ratios of bis-(4-hydroxyphenyl) sulfone to monoaldehyde, 
dialdehyde and/or glyoxylic acid or its alkali metal salt to unsubstituted 
or substituted aminoacetic acid or its salt of 1:0.5-4:0.3-4, the molar 
amount of aminoacetic acid or its derivative being less than or equal to 
the molar amount of aldehdye, dialdehyde and/or glyoxylic acid, in aqueous 
or aqueous alcoholic solution, if necessary in a closed system, at from 
20.degree. to 200.degree. C. and at a pH of from 3 to 12. 
Preferred condensates are obtained if 0.8-2.5 moles of aldehyde, dialdehyde 
or glyoxylic acid and 0.5-2 moles of aminoacetic acid or its derivatives 
are used per mole of bis-(4-hydroxyphenyl) sulfone, the molar amount of 
aminoacetic acid or its derivative always being less than or equal to the 
molar amount of aldehyde, dialdehyde or glyoxylic acid, at 
50.degree.-100.degree. C. under atmospheric pressure and at a pH of 4-8. 
Examples of aliphatic monoaldehdyes and dialdehydes are formaldehyde, 
acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, glyoxal, 
malondialdehyde, succindialdehyde, glutaraldehyde, and adipaldehyde. They 
are preferably used in the form of an aqueous solution. It is also 
possible to use their open-chain or cyclic acetals, or polymer forms, eg. 
paraformaldehyde. The preferred aldehydes are formaldehyde, in particular 
in the form of its roughly 30% strength by weight aqueous solution, and 
glyoxal in the form of the usual aqueous solution of about 40% strength by 
weight. 
Glyoxylic acid is used as the usual aqueous solution or as an alkali metal 
salt, in particular as the sodium salt of glyoxylic acid. It is also 
possible to use mixtures of glyoxylic acid and an alkali metal salt. 
Suitable N-substituted aminoacetic acids are iminodiacetic acid, 
ethanolaminoacetic acid, glycine, ethylenediamine-N,N-diacetic acid and 
sarcosine, in each case in the acidic form or in the form of an alkali 
metal salt, in particular a sodium salt, or the ammonium salt. It is also 
possible to use mixtures of the acid with a salt. A preferably used 
aminoacetic acid is iminodiacetic acid, and an alkali metal or ammonium 
salt, in particular the sodium salt, are also preferably used. 
Accordingly, the preparation of the condensates from bis-(4-hydroxyphenyl) 
sulfone, formaldehyde or glyoxal and iminodiacetic acid or a salt is 
particularly preferred. 
The starting compounds can be combined in any order. Advantageously, the 
three starting components are initially taken in aqueous solution and are 
heated. Mixtures of the abovementioned aldehyde compounds or amino acids 
can, if required, also be used. 
The preferred reaction medium is water. However, it is also possible to use 
aqueous alcoholic solutions employing lower, water-miscible alcohols, such 
as methanol, ethanol, n-propanol, isopropanol or a mixture of the stated 
alcohols, and, as a rule, 10-50% by weight, based on the weight of the 
water, of alcohol or alcohol mixture are added. Other water-miscible 
solvents which may be used are, for example, dioxane and acetonitrile. 
The reaction is advantageously carried out at a pH of 3-12, preferably 4-8. 
The desired pH may be obtained by adding a base or acid, preferably an 
aqueous solution of an alkali metal hydroxide or of a mineral acid. 
Temperatures of from 50.degree. to 100.degree. C. under atmospheric 
pressure are preferred. As a rule, the condensation is carried out at 
80.degree. C. 
The condensation reaction is carried out, i.e. the stirred reaction mixture 
is heated, until, at the pH set and the prevailing temperature, there is 
no further change in the viscosity and the starting compounds are no 
longer detectable by chromatography. 
In the condensation reactions described above, as a rule 10-80, preferably 
30-60, % strength by weight aqueous solutions of starting materials are 
reacted while stirring. The solutions obtained, which are advantageously 
brought to solids contents of 10-80, preferably 30-60, % by weight, can be 
used directly in practice. The condensates can be obtained in powder form 
without difficulties by a conventional method, such as distilling off the 
solvent or, for example, spray drying. 
The condensates are furthermore an excellent tanning assistant for tanning 
leather in conjunction with chromium-free mineral tanning agents, in 
particular with aluminum tanning agents. 
The present invention furthermore relates to a process for tanning leather 
in an aqueous liquor, wherein the pickled pelts are treated with a 
condensate of bis-(4-hydroxyphenyl) sulfone, a monoaldehyde, a dialdehyde 
and/or glyoxylic acid or its alkali metal salt and, if required, an 
N-substituted aminoacetic acid, if necessary in the form of an alkali 
metal salt or ammonium salt as described above and defined in the claims, 
in an amount of 4-20% by weight, based on the pelt weight, at 
20.degree.-50.degree. C., and then with an aluminum, zirconium or titanium 
compound as a mineral tanning agent in an amount of 4-16% by weight, based 
on the pelt weight, at 20.degree.-45.degree. C., the first and second 
stages being interchangeable, and the use of these condensates, as defined 
in the claims, as tanning assistants in conjunction with an aluminum, 
zirconium or titanium compound as a mineral tanning agent. 
Further information in this context is as follows: the starting material 
usually comprises pickled pelts, for example cattle pelts having split 
thicknesses of 1.5-4 mm. 
The aqueous liquor of the pickle bath is advantageously used in liquor 
ratios of 30-200%, preferably 50-100%. 
The condensates to be used according to the invention are usually added to 
the pickle bath. In the novel tanning process, a pH of 2-5, preferably 
2.5-4.0, is advantageously maintained in the first stage. The pH can be 
adjusted by adding, for example, sodium bicarbonate. 
As a rule, the condensate is added in two parts, and drumming is carried 
out for a total of from 1 to 18 hours. 
In the second stage, the mineral tanning agents used are, in particular, 
aluminum tanning agents, such as commercial aluminum sulfate or commercial 
basic aluminum chloride, for example with a basicity of about 65% and an 
alumina content of 22-23% or a basicity of about 20% and an alumina 
content of 16-18%. 
These are advantageously added in an amount of 4-16%, preferably 6-12%, 
based on the pelt weight. 
Drumming is carried out at 20.degree.-45.degree. C., preferably 
30.degree.-40.degree. C., for 1-18, preferably 4-14, hours. 
During incorporation of the mineral tanning agents by drumming, a pH of 
2.0-4.0 is advantageous. After the mineral tanning agent has been 
incorporated, the pH is, as a rule, brought to 4.5-6, preferably 4.5-5.5, 
by adding sodium formate, sodium acetate, sodium bicarbonate or magnesium 
oxide. 
When zirconium salts are used, the pH is, as a rule, not kept higher than 
2.5. 
As mentioned above, the two tanning stages can be interchanged in their 
order. The Examples which follow illustrate the invention. In the 
Examples, parts and percentages are by weight unless stated otherwise.

EXAMPLES 
Analysis: 
30% strength aqueous solutions of the condensates generally reach 
viscosities of from 10 to 500 mPa.s.sec.sup.-1. 
The IR spectra contain characteristic bands between 3450 and 2500 cm.sup.-1 
(OH--, COOH--, amine-, aromatic and aliphatic C--H stretching vibrations) 
and at 1630 cm.sup.-1 (COO.sup..crclbar. stretching vibrations). 
Below 300.degree. C., the defined melting point is not detectable. 
Preparation Examples 
EXAMPLE 1 
125 g (0.5 mole) of bis-(4-hydroxyphenyl) sulfone, 100 g (1.0 mole) of 30% 
strength aqueous formaldehyde and 133 g (1.0 mole) of iminodiacetic acid 
are mixed, and 300 g of water are added. The resulting suspension is 
subsequently heated to 80.degree. C., and the pH is then brought to 6.5 
with 25% strength sodium hydroxide solution. After the mixture has been 
stirred for 4 hours at 80.degree. C., HPLC and aldehyde titration are used 
to show that the starting materials are absent and there is no longer any 
change in the viscosity. After readily volatile components have been 
distilled off under reduced pressure of 30 mbar, an orange amorphous 
residue (249 g) is obtained. 
EXAMPLE 2 
125 g (0.5 mole) of bis-(4-hydroxyphenyl) sulfone 90 g (0.9 mole) of 30% 
strength formaldehyde and 52.2 g (0.4 mole) of iminodiacetic acid are 
mixed with 240 g of water. The experiment is continued similarly to that 
described under Example 1. A yellow amorphous residue (195 g) results. 
EXAMPLE 3 
Example 2 is repeated using a similar procedure; instead of iminodiacetic 
acid, its disodium salt is used in the form of a 30% strength aqueous 
solution. 
EXAMPLE 4 
250 g (1.0 mole) of bis-(4-hydroxyphenyl) sulfone are dissolved in 250 g of 
ethanol, and the pH is brought to 5.0 with 50% strength sodium hydroxide 
solution. A 40% strength aqueous solution of 104.4 g (0.8 mole) of 
iminodiacetic acid, which has been brought beforehand to pH 5.0 with 50% 
strength sodium hydroxide solution, and 130 g (1.3 moles) of a 30% 
strength formaldehyde solution are together added dropwise to this 
solution at 80.degree. C. in the course of 3 hours. Thereafter, stirring 
is continued for a further hour at 80.degree. C., after which HPLC and 
viscosity measurement show that the reaction has ended. After the solution 
has been concentrated and the solvent distilled off under reduced 
pressure, 351 g of an orange solid remain. 
EXAMPLE 5 
The procedure is similar to that of Example 1, using 125 g (0.5 mole) of 
bis-(4-hydroxyphenyl) sulfone, 75 g (0.75 mole) of 30% strength 
formaldehyde and 99.8 g (0.75 mole) of iminodiacetic acid at pH 6. 
EXAMPLE 6 
The Example is carried out similarly to Example 1, using 125 g (0.5 mole) 
of bis-(4-hydroxyphenyl) sulfone, 65 g (0.65 mole) of 30% strength 
formaldehyde and 79.8 g (0.6 mole) of iminodiacetic acid at pH 6.5. 
EXAMPLE 7 
The experiment is carried out similarly to Example 1, using 125 g (0.5 
mole) of bis-(4-hydroxyphenyl) sulfone, 65 g (0.65 mole) of 30% strength 
formaldehyde and 66.5 g (0.5 mole) of iminodiacetic acid at pH 6. 
EXAMPLE 8 
The procedure is similar to that of Example 1, using 50 g (0.2 mole) of 
bis-(4-hydroxyphenyl) sulfone, 30 g (0.4 mole) of 30% strength 
formaldehyde and 21.3 g (0.16 mole) of iminodiacetic acid in 120 g of 
water at pH 5.5. 
EXAMPLE 9 
125 g (0.5 mole) of bis-(4-hydroxyphenyl) sulfone, 100 g (1.0 mole) of 30% 
strength aqueous formaldehyde and 133 g (1.0 mole) of iminodiacetic acid 
are mixed with 250 g of water and 250 g of ethanol, and the mixture is 
brought to pH 5.5 with 50% strength aqueous sodium hydroxide solution. The 
mixture is heated at the boil for 6.5 hours. After the volatile components 
have been distilled off under reduced pressure and the residue has been 
dried, 265 g of a yellow solid product remain. 
EXAMPLE 10 
Example 9 is repeated in a similar manner using 125 g (0.5 mole) of 
bis-(4-hydroxyphenyl) sulfone, 90 g (0.9 mole) of 30% strength aqueous 
formaldehyde and 53.2 g (0.4 mole) of iminodiacetic acid. 189 g of 
condensate result. 
EXAMPLE 11 
Example 9 is repeated in a similar manner using 125 g (0.5 mole) of 
bis-(4-hydroxyphenyl) sulfone, 100 g (1.0 mole) of 30% strength aqueous 
formaldehyde and 53.2 g (0.4 mole) of iminodiacetic acid. After the 
mixture has been concentrated and the residue dried, 195 g of condensate 
remain. 
EXAMPLE 12 
The experiment is carried out similarly to Example 9, using 125 g (0.5 
mole) of bis-(4-hydroxyphenyl) sulfone, 65 g (0.65 mole) of 30% strength 
aqueous formaldehyde and 53.2 g (0.4 mole) of iminodiacetic acid. 185 g of 
condensate are obtained. 
EXAMPLE 13 
108.8 g (0.75 mole) of 40% strength aqueous glyoxal and 53.2 g (0.4 mole) 
of iminodiacetic acid are initially taken. The pH is brought to 6.5 with 
50% strength aqueous sodium hydroxide solution. Thereafter, the mixture is 
heated to 80.degree. C. and a solution of 125 g (0.5 mole) of 
bis-(4-hydroxyphenyl) sulfone in 250 g of ethanol is added dropwise in the 
course of 1 hour. 
Stirring is then carried out for a further 5 hours at 80.degree. C. 
Thereafter, by means of aldehyde determination and chromatography, it is 
shown that the starting materials are absent and furthermore that there is 
no change in the viscosity. After the volatile components have been 
removed and the residue dried under reduced pressure, 194 g of condensate 
are obtained. 
EXAMPLE 14 
The experiment is carried out similarly to Example 13, using 66.6 g (0.45 
mole) of 50% strength aqueous glyoxylic acid instead of glyoxal, 26.6 g 
(0.2 mole) of iminodiacetic acid and 62.5 g (0.25 mole) of 
bis-(4-hydroxyphenyl) sulfone. After a total reaction time of 10 hours, 
the volatile components are distilled off and 115 g of condensate are 
obtained. 
EXAMPLE 15 
Example 13 is repeated in a similar manner, using 36.3 g (0.25 mole) of 40% 
strength glyoxal and 37 g (0.25 mole) of 50% strength aqueous glyoxylic 
acid instead of glyoxal. After a total reaction time of 8 hours, 195 g of 
condensate are obtained. 
USE EXAMPLES 
Use Example 1 
100 parts of cattle pelts (split thickness 2.0 mm) are treated in a pickle 
bath consisting of 60 parts of water, 6 parts of sodium chloride, 0.6 part 
of formic acid and 0.6 part of sulfuric acid for 60 minutes. 
A solution of 10 parts of the 100% pure condensate from Preparation Example 
3, which has been diluted, at pH 4.0, with 90 parts of water, is added to 
this pickle bath at room temperature in two portions with an interval of 
90 minutes, and drumming is carried out for a further 90 minutes. 
Thereafter, 10 parts of a commercial aluminum chloride tanning agent 
(basicity 20%, Al.sub.2 O.sub.3 content 16-18%) are added to the liquor, 
which is agitated overnight. Next morning, the pH of the liquor is from 
2.1 to 2.3. 2 parts of sodium acetate are added and drumming is carried 
out for a further 60 minutes. 
The temperature is then increased to 40.degree. C., and the pH of the 
liquor is brought to 5.6 in the course of 6 hours by adding a total amount 
of 1.7 parts of magnesium oxide a little at a time. 
The leathers are stored overnight. Thereafter, fatliquoring, acidification 
and finishing are carried out in 100 parts of fresh liquor. The leather 
has a shrinking temperature of 92.degree. C. and is pale cream and very 
soft. It possesses good lightfastness and heat resistance. 
USE EXAMPLE 2 
10 parts of a commercial aluminum chloride tanning agent (basicity 20%, 
Al.sub.2 O.sub.3 content 16-18%) are added to 100 parts of cattle pelts, 
pickled according to Use Example 1, in 60 parts of pickle liquor, and are 
incorporated by drumming at room temperature (25.degree. C.) for 4 hours. 
Thereafter, a solution of 10 parts of the 100% pure condensate from 
Preparation Example 3, which has been diluted, at pH 4, with 90 parts of 
water, is added in 2 portions with an interval of 90 minutes, and the 
mixture is agitated overnight. Next morning, the liquor has a pH of 2.2. 
The pH is brought to 2.6 with 2 parts of sodium acetate and drumming is 
carried out for 60 minutes. The pH is then brought to 5.5 in the course of 
6 hours with 1.7 parts of magnesium oxide at 40.degree. C. The leathers 
are finished in the conventional manner. 
After fatliquoring, they have a shrinking temperature of 92.degree. C., are 
soft and pale and have good resistance to light and heat. 
USE EXAMPLE 3 
If, instead of the condensate stated in Preparation Example 1, the came 
amount of the condensate from Preparation Example 8 is used, similarly 
pale and soft leathers are obtained. They have a shrinking temperature of 
94.degree. C. In this case too, the leathers have good lightfastness and 
heat resistance. 
USE EXAMPLE 4 
If, instead of the 1.7 parts of magnesium oxide stated in Use Example 1, 
only 1.4 parts are used, the final pH obtained is 4.7. The leathers have a 
shrinking temperature of 91.degree. C., are soft and pale and have good 
lightfastness and heat resistance. 
USE EXAMPLE 5 
Instead of the aluminum tanning agent stated in Use Example 1, 8 parts of 
another commercial aluminum tanning agent (basicity 65%, Al.sub.2 O.sub.3 
content 22-23%) are used. 
The leathers prepared therewith, after they have been fatliquored, have a 
shrinking temperature of 92.degree. C., are pale and soft and have good 
lightfastness and heat resistance. 
USE EXAMPLE 6 
If, instead of the condensate from Preparation Example 3, mentioned in Use 
Example 1, the same amount of the condensate from Preparation Example 2 is 
used, the leathers have a shrinking temperature of 90.degree. C. after 
fatliquoring. They possess good lightfastness and heat resistance. 
USE EXAMPLE 7 
If, instead of the 1.7 parts of magnesium oxide stated in Use Example 1, 
6.2 parts of sodium bicarbonate are used in the same period and the 
procedure is carried out at room temperature (25.degree. C.), a final pH 
of 5.4 is obtained. After fatliquoring, the leathers have a shrinking 
temperature of 90.degree. C. and possess good resistance to light and 
heat.