DE1668548B1 - Process for the partial esterification of cellulose with organic acids while maintaining its shape and structure - Google Patents

Description

For the esterification of native or regenerated cellulose in a heterogeneous system while maintaining the The form and structure of cellulose are primarily used with carboxylic acid anhydrides and acid chlorides. Of all the esterification processes, partial acetylation is already of technical importance got.

The reaction between cellulose and acetic acid hydride is both acidic and basic Catalysis accessible. The general rule here is that the acid-catalyzed acetylation occurs relatively low temperatures, the base catalyzed at temperatures above 100 ° C is carried out.

Preferred catalysts for the partial esterification of cellulose are HClO ₄ , H ₃ PO ₄ or H ₂ SO ₄ on the one hand or alkali acetates or alkali salts of weak organic acids on the other.

The acetylation of cellulose while maintaining its shape and structure can be carried out in the acetic acid / Acetic anhydride is only used for limited acetylation because the partially acetylated cellulose is from one certain degree of acetylation to swell and finally to go into solution.

The acetylation of cellulose without the use of catalysts succeeds when heating cellulose in acetic acid / acetic anhydride under pressure at temperatures above 135 ° C or when used a mixture of acetic acid with trifluoroacetic anhydride at room temperature.

A precondition for the partial acetylation of cellulose in the liquid phase is prior swelling in water and the subsequent solvent exchange with glacial acetic acid, making this process with are burdened with high costs.

Processes are also known for carrying out the acetylation of cellulose in the gas phase. For this the cellulose is impregnated with an aqueous catalyst solution (mainly sodium acetate) first freed from water by drying or by the action of acetic acid vapor and then treated with acetic anhydride vapors.

The esterification with the chlorides of carboxylic acids and sulfonic acids generally proceeds in organic solvents and requires a pretreatment of the cellulose with strong caustic soda, whereby this process is based at most on a partial esterification of native, i. H. Sufficiently more alkali-resistant Limit cellulose. Because of the high costs, these procedures could not be used Introduce practice.

The partial esterification of cellulose with derivatives of cyanuric chloride, des Tetrachloropyrimidine, dichloroquinoxaline and others, in that these reactions lead to the reactive coloring of Cellulose were used.

The partial esterification of cellulose aroused great interest after it had already been recognized Partial esterification of the cellulose with degrees of substitution of 0.5 to 1 is sufficient to make the cellulose valuable To give properties. So z. B. a partial acetylation of cellulose in this order of magnitude, to bring about resistance to bacteria and mold and the temperature resistance as well as to significantly improve the resistance to the effects of weather or seawater.

The invention relates to a process for the partial esterification of cellulose with organic acids while maintaining its shape and structure, which is characterized in that the cellulose is impregnated with an aqueous solution of alkali salts of S-acylated mercaptocarboxylic acids, dried for 1 minute to 72 hours 100 to 200 ^° C., preferably 5 minutes to 2 hours, ^{heated to 130 to 170 °} C., washed out and dried.

The partial esterification of cellulose by the salts of the acyl mercaptocarboxylic acids does not result in any volatile compounds, so that the process in open systems and on conventional machines textile finishing on the one hand and the production of foils or paper on the other can be.

For the preferred execution of the method, fibers, threads, yarns or those made therefrom are used Textiles and nonwovens that are partially or completely made of native or regenerated cellulose, soaked with an aqueous solution of the salt of an S-acylated mercaptocarboxylic acid, excess Solution spun off or squeezed out by rollers, dried and then heated. To the distance of the resulting mercaptocarboxylic acid salt and unreacted starting compound Washed cold and aftertreated in the usual way depending on the type of cellulose-containing material and dried. The higher the condensation temperature, the shorter the required reaction time, however, the greater the risk of a color change in the cellulose. Depending on the article or Purpose of use, therefore, the reaction time and reaction temperature must be reasonably matched to one another, to get optimal effects. The esterification of the cellulose that occurs at the same time has an effect declining temperature sensitivity has a positive effect on the tendency to yellowing of the material.

The acyl mercaptocarboxylic acids can also be used as a paste-like, aqueous paste of their salts on the Cellulose are applied.

The achievable degree of esterification (average degree of substitution, abbreviated to D.S.) of the cellulose by the method of the invention is limited on the one hand by the water solubility of the used Salts, on the other hand due to the liquor absorption of the shaped bodies made of cellulose after impregnation, that is, the amount of reactive substance applied per unit weight of cellulose. One achieves with a single application of the method according to the invention, DS values of 0.3 to 1.0. There however, the physical and chemical properties of cellulose, even through slight esterification can be influenced considerably, the practical importance of the method is great.

The rate of transesterification of the acyl mercaptocarboxylic acids by cellulose is increasing Concentration of impregnation solutions as well as decreasing with increasing liquor uptake. Both influences can by lengthening the reaction time and / or by increasing the reaction temperature be compensated within certain limits. To achieve higher degrees of substitution of the esterified Cellulose can be used the process of the invention several times in succession. Included can also transfer different acyl residues one after the other to cellulose, i. H. mixed esters of cellulose getting produced.

In the production of mixed esters of cellulose from acids of very different molecular weights It is best to start with the higher acidity

To esterify molecular weight. The production of partial mixed esters of cellulose can also be done by Solutions are made that contain mixtures of acylated mercaptocarboxylic acids containing various acyl radicals contain. Because the removal of excess impregnation solution from fiber material by centrifuging is generally not as possible as by pressing impregnated flat structures, In the esterification reactions on flake, the yield is lower compared to textiles. It is recommended in any case, with the impregnation liquor to remove introduced water by a drying process that takes place as quickly as possible. Drying and implementation are sensibly combined by using the impregnated Material is entered moist in the boiler room, which has been brought to reaction temperature.

The esterification of the cellulose according to the process of the invention takes place under optimal conditions in yields of over 70% of theory, based on the amount of acyl derivative taken up. the Type of acyl radical and the type of mercaptocarboxylic acid used to transfer the acyl radical exert a significant influence on the achievable yield. .

The achievable yields in the esterification of the cellulose also depend on the reactivity cellulose dependent. The lower the orientation of the cellulose macromolecules, the more so The willingness to react and thus the yield in esterification reactions is greater. Therefore the yield from the esterification of native cellulose is lower than that of regenerated cellulose. Normal Spun rayon with a relatively low orientation can in turn be acylated with a higher yield than fiber types, for example with an extremely high level of order of cellulose, such as. B. Fibers with low wet deformability (Viscose wool with a high wet modulus).

Crosslinking occurs during esterification with diesters of mercaptocarboxylic acids and dicarboxylic acids the cellulose through bifunctional esterification, creating high crease angles in the fabric can be obtained and the Cuoxam solubility of the cellulose is canceled. On the other hand you can Monoester of mercaptocarboxylic acids and dicarboxylic acids with success for the introduction of acid groups be used in the cellulose, whereby z. B. improved dyeability with basic dyes results.

The acylated salts suitable for the partial esterification of cellulose by the process of the invention Mercaptocarboxylic acids can be described by the following general formulas:

1. Mercaptocarboxylic acids acylated with monocarboxylic acids:

R ₁ -CO-SR ₂ -COOMe

R ₁ = any monovalent organic radical, R ₂ = any divalent organic radical, Me = alkali metal.

2. Mercaptocarboxylic acids acylated with dicarboxylic acids:

MeOOC-R ₁ -S-CO-R ₂ -CO-SR ₁ -COOMe

or

MeOOC-

R ₁ -S-CO-R ₂ -COOMe

R ₁ and R ₂ = any divalent organic

Leftovers,
Me = alkali metal.

The acylated mercaptocarboxylic acids have the advantage that they are easily accessible preparatively. Mercaptocarboxylic acids can in numerous cases in aqueous-alkaline solution with high yields be acylated by acid chlorides or acid anhydrides. Remarkably, the Acylation of mercaptocarboxylic acids with acid chlorides or acid anhydrides resulting aqueous Solutions can be used without further purification for the partial esterification of cellulose, whereby Chemical losses are kept to a minimum.

The alkali salts of the acylated mercaptocarboxylic acids formed are of low molecular weight of the mercaptocarboxylic acid are often extremely soluble in water and allow them to be produced in a more concentrated manner Solutions, whereby relatively high degrees of substitution are achieved when they are implemented with cellulose can. The salts of acylated mercaptocarboxylic acids are practical in aqueous solution Sufficiently durable.

In many cases there is hardly any hydrolytic cleavage of the even during transesterification with cellulose Acyl mercaptocarboxylic acids instead, so that with appropriate solubility ratios from the wash water, with which the shaped bodies made of cellulose are treated after the esterification reaction has taken place, the free acyl mercaptocarboxylic acids can be recovered unchanged.

The variety of modifiability of cellulose by the process of the invention results from the Possibility of using any organic molecules with at least one carboxyl group according to known methods first to convert into the esters of the mercaptocarboxylic acids and these as salts in aqueous To implement solution with cellulose. In this way, molecules can be introduced into cellulose, the halogens, Contain nitrogen, sulfur, etc., thereby reducing the chemical and physical properties of the Cellulose can be subjected to numerous changes.

The following examples illustrate the invention. The yields given relate to that recorded Amount of acyl derivative.

60 Example 1 a) Preparation of the starting solutions

140 g of NaOH were dissolved in 556 ml of water and 170 g of 95% strength thioglycolic acid were added with stirring. The resulting solution was stirred at a temperature not exceeding + 10 ° C 246 g of benzoyl chloride were added dropwise. 1 kg of neutrally reacting solution was obtained, the next

NaCl contained 1.75 mol of benzoylthioglycolic acid as the sodium salt (solution I).
343 grams of benzoylthioglycolic acid

C ₆ H ₅ COS-CH ₂ -COOH

% Fleets
recording % Benzoin
acid
in the product % Yield Solution I.
Solution II 189
165 23.8
27.0 79
100

were dispersed in 520 ml of water at room temperature and 92.8 g of Na ₂ CO ₃ were added in portions with stirring. When the addition was complete, the mixture was made up to 1 kg with water. The solution contained 1.75 moles of benzoyl thioglycolate (solution II).

b) cellulose esterification

Desized, dried fabrics made from commercially available matted viscose wool 2.75 denier (plain weave; warp like weft Nm 34/1; shedding: four shafts; weight of raw material: 166 g / m ² ) were once with solution I and the other with solution II soaked, pressed and heated ^{to 130 °} C. on a tenter for 39 hours. The fabrics were washed and dried exhaustively. They resulted in the following analysis: The swelling value of the fabric fell from 74% of an equally treated blank sample to 39%. The partially benzoylated cellulose only stained with direct dyes, but could be dyed in deep shades with dispersion and basic dyes.

Example 2

According to Example 1, cellulose fabrics with NaCl-free solutions of benzoylthioglycolic acid were various Concentration impregnated, squeezed to different liquor uptake and different Times heated to different temperatures. Table 1 shows the influence of the concentration the benzoyl thioglycolate solution (2 a to 2d), the time (2e to 2i), the liquor uptake (2j to 2 m) and the temperature (2n to 2q) on the achievable yield in the benzoylation of cellulose.

Tabel

attempt concentration % Liquor pick-up reaction time Reaction
temperature % Benzoic acid
in the product % Yield Moles / kg hours ⁰ C 2a 2.55 175 1 150 22.6 61 2 B 1,786 175 1 150 19.2 67 2c 1.276 179 1 150 16.8 75 2d 0.764 174 1 150 12.7 90 2e 2 172 2 130 16.0 52 2f 2 172 6th 130 20.0 65 2g 2 164 15th 130 23.2 78 2h 2 175 25th 130 25.65 82 2i 2 160 68 130 26.8 92 2y 1.75 146 2 150 22.2 90 2k 1.75 171 2 150 26.5 96 21 1.75 191 2 150 26.5 88 2m 1.75 219 2 150 25.8 78 2n 2 175 4th 120 13.6 44 2o 2 175 4th 130 17.4 56 2p 2 175 4th 140 21.5 69 2q 2 175 4th 150 26.6 85 ■

Examples 3 to 10
a) Production of the raw materials

Those used in these examples, S-acyl-thioglycolic acids were prepared according to the generally valid operation: 1 mole of thioglycolic acid was added with 2 mol of NaOH in aqueous solution, cooled to 0 to 10 ⁰ C and 1 mole of monocarboxylic acid chloride and 0.5 mol of dicarboxylic acid chloride added dropwise with stirring. The end of the reaction was recognized by the neutral reaction of the previously alkaline solution. The amount of water used to dilute the thioglycolate solution was chosen so that the neutral solution formed after the addition of the acid chloride did not contain any undissolved fractions.

The neutral one, containing the S-acyl thioglycolate Solution was precipitated with 16% hydrochloric acid in a molar ratio of 1: 1 and the S-acylthioglycolic acid was filtered off with suction, Washed free of chloride with cold water and dried. The yields were between 70 and 90% of theory.

The degree of purity of the S-ethylthioglycolic acids was checked by determining the equivalent weight and the saponification number. If necessary, was the crude S-acyl-thioglycolic acid depending on its solubility recrystallized from water or suitable organic solvents.

In Example 9, carbomethoxymercaptoacetylthioglycolic acid was used to prepare Reacted 2 moles of thioglycolic acid and 4 moles of NaOH with 1 mole of chloroacetyl chloride, which is readily water-soluble Reaction product extracted from the acidified solution with ether and removed by distilling off the dried Ether solution isolated.

b) Cellulose esterification:

The thioglycolic acid derivatives were available as aqueous

Solutions of their sodium salts on cellulose tissue according to Example 1 applied, pressed and reacted by heating. The terms and results are summarized in table 2:

Table 2

at
game derivative solution
Moles / kg Fleets
on
took Reak
tion time
hours React
functional
tempe-
rature
-c Bound acid residue % ge
bound
acid
in the
product Consum.
ml 0.1 n-
NaOH per
Gram
dry
tissue the end
prey 3 Acetylthipglycolic acid 3.2 145 1 150 CH ₃ CO - 12.75 - 55 4th Cyproylthioglycolic acid 1.5 114 1 150 C ₅ H ₁₁ CO - 11.55 - 70 5 Stearylthioglycolic acid 0.047 112 1 150 C ₁₇ H ₃₅ CO- 1.40 - 95 OH 6th Acetylsalicoylthioglycolic acid 1 154 2 120 oC _Ä
co 17.3 12.5 96 co— o-CA
co 7th o-phthaloyldithioglycolic acid 1 122 1 150 co— 10.0 - 57 P-CA
co— 8th Terephthaloyldithiol glycol
acid 0.21 162 4th 130 -COCH ₂ • S • CH ₂ • COONa 3.65 - 63 9 Carbomethoxy mercapto-
acetylthioglycolic acid 1.84 183 1 150 -COCH ₂ -CH ₂ -CO- 25.6 14.9 67 10 Succinoyldithioglycolic acid 0.8 213 4th 130 8.4 - 48

Example 11
a) Preparation of the starting solutions

436 g of 95% thioglycolic acid were dissolved in 900 ml of water and 0.9 l NaOH (400 g / l NaOH) offset. 450 g of succinic anhydride were added to the solution, which had cooled to room temperature, the mixture heated to 30 to 35 ° C and the anhydride gradually went into solution. The weight of the solution was made up to 3 kg with water, the 1.5 mol / kg succinoylmonothioglycolic acid as Na-SaIz

(NaOOC · CH ₂ · CH ₂ -CO-S- CH ₂ · COONa)

contained (solution I).

An intimate mixture of 864 g succinoylmonothioglycolic acid

HOOC • CH ₂ • S • CO • CH ₂ • CH ₂ • COOH

(prepared by acidifying an appropriate amount of solution I with HCl, suction, washing with a little ice-cold water and drying) and 755 g of NaHCO ₃ were added to 1.75 l of water with stirring and water cooling and, after the _{evolution of CO 2 had ended,} with water topped up to 3 kg. The solution contained 1.5 mol / kg succinoylmonothioglycolic acid as Na salt (solution II).

b) cellulose esterification

Tissues according to Example 1 were soaked once with solution I and the other with solution II, squeezed off and heated on a tenter at 140 ° C for 4 hours, washed and dried. The analysis showed the following results; where the bound acid as

COOH • CH ₂ • CH ₂ • COONa

was calculated:

55 Solution I.
Solution II % Fleets
recording % bonded
acid
in the product % Yield 197
194 19.1
17.9 63
60

After the partial esterification, the fabric had a swelling value of 84% (previously 80%) and contained direct dyes and disperse dyes cannot be dyed, but can be dyed with basic dyes.

The following crease angles were measured on the fabrics treated with solution I (dry: Loaded 1 hour, measured 1 hour after unloading. Wet: Loaded 3 minutes, 3 minutes after unloading measured):

109 519/374

Chain .
Shot

Starting tissue

dry

85
90

wet

75
100

Partially esterified
tissue

dry

115
117

wet

82
120

The low crease angle and the high swelling value of the partially esterified fabric show that no cross-linking of the cellulose has occurred.

10

Examples 12-14

Desized cellulose tissue according to Example 1 was mixed with aqueous solutions of the sodium salts S-benzoyl mercaptocarboxylic acids, the preparation of which was also carried out analogously to Example 1, impregnated, pressed, dried and reacted at elevated temperature.

The test conditions and results are ίο contained in Table 3:

Tabel

example derivative solution % Fleets
recording reaction time Reaction
temperature % Benzoin
acid yield
% the Moles / kg (Minutes) ⁰ C in the product theory 12th S-benzoylthiosalicylic acid 1.0 128 30th 150 8.53 62 13th S-benzoyl-a-mercapto- 1.09 119 75 150 5.59 40 valeric acid 14th S-benzoyl-ß-mercapto- 1.73 110 3 200 5.2 27 propionic acid

Claims (6)

Patent claims: 1. A process for the partial esterification of cellulose with organic acids while maintaining its shape and structure, characterized in that the cellulose is impregnated with an aqueous solution of alkali salts of S-acylated mercaptocarboxylic acids, dried for 1 minute to 72 hours at 100 to 200 ^° C , preferably heated for 5 minutes to 2 hours at 130 to 17O ⁰ C, washed out and dried. 2. The method according to claim 1, characterized in that the cellulose is impregnated with an aqueous solution of alkali salts of S-benzoylated mercaptocarboxylic acids or of mono- or diesters of mercaptocarboxylic acids and dicarboxylic acids, preferably of S-ethylthioglycolic acids. -.- ■ 3. The method according to claim 1 or 2, characterized in that the impregnation and Repeated heating, if necessary also washing and drying, several times. 4. The method according to claim 3, characterized in that the individual impregnations with alkali salts of S-acylated mercaptocarboxylic acids containing various acyl radicals. 5. The method according to any one of claims 1 to 3, characterized in that the impregnation of cellulose with mixtures of alkali salts containing various acyl radicals S-acylated Performs mercaptocarboxylic acids. 6. The method according to any one of claims 1 to 5, characterized in that the cellulose with impregnated with an unpurified solution of alkali salts of S-acylated mercaptocarboxylic acids, those in the reaction of mercaptocarboxylic acids with alkali salts with acid chlorides or acid anhydrides has been received.