GB2132202A - Process of preparing alkylsaccharides - Google Patents

Abstract

A process for producing an alkylsaccharide comprises reacting an alcohol with a reducing sugar containing from 5 to 6 carbon atoms, or source thereof, in the presence of a strong acid catalyst, characterised in that from 0.0015 to 1% of hydroxy polycarboxylic acid, selected from citric acid, maleic acid, tartaric acid, and mixtures thereof is incorporated in the reaction mixture. This provides an alkylsaccharide product with improved colour.

Description

SPECIFICATION Process of preparing alkylsaccharides This invention relates to an improved process for making alkylsaccharides in which the alkyl group contains from 1 to 20 carbon atoms and the saccharide portion contains from 1.5 to 30 saccharide units. The improved process provides an alkylsaccharide product with improved color.

U.S. Patent 4,341,809, discloses a stablilized starch composition prepared by adding a bufferto a slurry of starch and then drying the starch-buffer slurry. All of the materials taught are alkaline to protect against acid degradation.

The present invention relates to a process for preparing an alkylsaccharide. It has been discovered that hydroxypolycarboxylic acids added at low levels, either during the formation of the alkylsaccharide or later during the subsequent cleanup processes, minimizes the formation of colored materials.Thus, the invention relates to the process for producing an alkylsaccharide by reacting an alcohol and a reducing sugar containing from Sto 6 carbon atoms, or source thereof, in the presence of a strong acid catalyst comprising adding to the reaction mixture from 0.0015% to 1% preferably from 0.0075% to .1%, more preferably from 0.02 to 0.05% of a hydroxy polycarboxylic acid based on the weight of reaction mixture preferably in the form of a hydrate and/or the process for hearing an alkylsaccharide in the presence of from 0.003% to 2%, preferably from 0.02% to 0.2%, more preferably from 0.04% to 0.1 % of a hydroxy polycarboxylic acid, or salt thereof, selected from citric acid, tartaric acid, maleic acid and mixtures thereof.

Processes for making the alkylsaccharides ofthis invention are described in U.S. Patent; 3,219,656 Boettner; 3,598,865, Lew; 3,707,535, Lew; 3,772,269, Lew; and 3,839,318, Mansfield. A preferred process is disclosed in European PatentApplication 83,200,572.2, Publication No.0092875 published 2 November 1983.

When the hydroxypolycarboxylic acids, or salts thereof, are incorporated into the reaction mix, preferably in the form oftheir hydrates, the color of the resulting alkylsaccharide is improved. Although it is not desired to be bound bytheory, itis believed that these hydroxypolycarboxylic acids act as buffers and water sinks and, when used as hydrates, sources of controlled water addition.

Afterthe preparation ofthe alkylsaccharide and neutralization of the acid catalyst used in the form tion of the alkylsaccharide, the hydroxypolycarboxylic acids ortheir salts act as buffering agents in any subsequent processing steps. By maintaining the pH of the alkylsaccharide within a range of from 3 to 10, preferably from 5 to 7, excess degradation ofthe alkylsaccharide and formation of color bodies is minimized even when the alkylsaccharide is exposed to high temperatures, e.g. from 1 lotto 165"C.

The alcohols useful in the formation of the alkylsac charides ofthis invention include fatty alcohols containing from one to 20 carbon atoms which can be primaryorsecondaryalcoholshavingstraightor branched chains which can be either saturated or unsaturated and may contain ether linkages. Preferably the alcohols are primary saturated alcohols including as specific examples, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, octyadecyl alco holland mixturesthereof. The preferred fatty alco- hols are those containing from 10 to 16 carbon atoms.

However, in addition to these longer chain fatty alcohols, shorter chain alcohols, such as methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, and glycerine can be used and, in fact, are desirable for many uses. The alcohol can also contain benzene rings so thatthe alcohol can be a phenol.

The saccharide portion of the molecule can be derived from frusctose, glucose, mannose, cylose, osose, lyxose, ribose and mixtures thereof. The preferred saccharides are glucose and fructose due to their availability and low cost and most preferred saccharide is derived from glucose. Preferably the reaction to form the alkylsaccharide is carried out at a temperature of from 90 to 130"C. Preferably the temperature is kept below 1 20"C to minimizeformation of color materials.

Auxiliary solvents can be used, includingtoluene, 08-12 hydrocarbons, etc.

Preferably the reaction takes place in a thin-film, preferably at high Reynolds numbers to permit a rapid reaction and improved heat transfer, thereby minimizing the time to which the saccharide is exposed to high temperatures. Thin-films can be achieved in wipedfilm evaporators, drum evaporators or mills in which two cylinders combine to form a thin film.

Acid catalysts useful inthepreparationofalkylsac- charides include such conventional acids as sulfuric, hydrochloric, phosphoric, phosphorus,toluenesulfo- nic, etc. Other Lewis acid catalysts can be used.The amount of acid catalyst used in normally between .001 and .1 moles per mole of saccharide monomer, preferably between .005 and .05, most preferably between .005 and .025. The amount of catalyst used can control the speed of reaction. Sulfuric acid is the preferred catalyst.

All ratios, percentages, and parts herein, are by weight unless otherwise specified. EXAMPLE 1 Alkylpolysaccharideswere prepared by combining 1 00g. of anhydrous dextrose; 1 65g. of fatty alcohols containing primarily 12 or 13 carbon atoms; 4039. of butanol; 0.529. p-toluene sulfonic acid; and the indicated acids which were added after the dextrose.

The reaction mixes were quickly heated to butanol's boiling point about 115-118 C (239-244 F) and allowed to refluxfor one hour. Then, the butanol was removed by partial vacuum at a minimum temperature of 93"C (200"Fj. Vacuum was increased to 2 mm Hg. and thetemperature allowed to rise to 1 1 50C (239"F) for 30 minutes. The reaction mix was then cooled and neutralized with 0.27g sodium carbonate dissolved in 2.59 H20. The percent transmission (Coleman Colorat470 nm in a 25 x 105 nm cell of a 50% solution in butanol) was measured.

% Transmission A. Control (no acid added) 27 B. 5.5g.citricacidhexahydrate 48 C.* 3.91g.tartaricacid 43 D.* 2.76g. maleicacid 47 *centrifuged to remove haze.

As can be seen from the above, the presence ofthe acids improves the colon When the alkylpolysaccharide product is exposed to a temperature of above 1 20"C in subsequent processng steps, including distillation of the unreacted fatty alcohol, similar results are obtained in that the products admixedwith the citric, tartaric, and/or maleic acids discolor much more slowly.

Claims (6)

1. A process for producing an alkylsaccharide by reacting an alcohol with a reducing sugar containing from 5 to 6 carbon atoms, or source thereof, in the presence of a strong acid catalyst, characterised in thatfrom 0.0015 to 1% of hydroxy polycarboxylic acid, selected from citric acid, maleic acid, tartaric acid and mixturesthereofis incorporated in the reaction mixture.

2. A process according to Claim 1 wherein said hydroxypolycarboxylic acid is present at a level of from 0.0075% to 0.1%, preferablyfrom 0.02% to 0.05%.

3. A process according to either one of claims 1 and 2 wherein said hyd roxypolycarboxylic acid is present in theform of a hydrate initially.

4. A process of heating an alkylsaccharide wherein the saccharide portion of said alkylsaccharide is derived from a reducing sugarcontaining five to six carbon atoms, characterised in that from 0.003 to 2% of a hydroxy polycarboxylic acid selected from citric acid, tartaric acid, maleic acid, and mixtures thereof is incorporated in the alkyl saccharide.

5. A process according to Claim 4 wherein the mixture ofthe alkylsaccharide and hydroxypolycarboxylic acid has a pH from 3 to 10, preferablyfrom 5 to 7.

6. A process according to either one of claims 4 and 5 wherein the alkylsaccharide is heated to from 100to165"C.