NEW REACTIONS OF PROPYLENE GLYCOL ALGINATE 455 possible, and mixtures with PVA or starch appear the most promising. Although insoluble, these reaction products swell in water and allow the passage of water vapour. Furthermore the PGA-starch product is broken down by enzymes and is therefore likely to be quite acceptable in food products. The thickening and suspending effects have not yet found commercial use, but the wide range of composition that can be used and of the consis- tencies that can be obtained suggest that the effect could provide a solution to a problem in formulation in some industrial field, possibly in cosmetics. (Received: 1st August 19691 REFERENCES (1) Steiner, A. B. and McNeely, \¾. H. Organic esters of alginic acid. Ind. Eng. Chem. 43 2 053 (1959). (2) Weissbach, A. and Hurwitz, J. The formation of 2-keto-3-deoxyheptonic acid in extracts of Escherichia coli B. J. Biol. Chern. 234 705 (1959). (3) Brit. Pat. 768 309: Process for the production of amides of alginic acid. (4) Brit. Pat. 962 483: Water insoluble film forming nitrogenous products. (5) Brit. Pat. 987 797: Improved method of hardening photographic silver halide material. (6) Brit. Pat. 1 135 856: A method of modifying alkylene glycol alginates. (7) Brit. Pat. 890 083: Acylation of hydroxy compounds with vinyl esters. DISCUSSION M•. G. A. GR•N•: Can you speculate on the nature of the chemical reaction occurring? We have discussed this matter several times and it is difficult to find out exactly what is happening chemically - the effects are so strange you would not expect them at all. T•F• L•cxuR•: From the nature of the products obtained, I think there must be some cross-linking. We must remember that in most cases the product obtained is broken down if the mixture remains alkaline, which suggests that it may be an ester. Various transesterification reactions have been described but they are normally done in anhydrous conditions, generally with an acid catalyst and it seems rather extraordinary that it could happen in dilute aqueous solutions or with an alkali. Not long ago I had my attention drawn to some patents on the acetylation of starch where vinyl acetate toohomer is reacted with starch which is suspended in sodium carbonate solution, and I wonder whether something similar could be happening here. I think there are a number of quite independent reactions going on. They probably all have different energies of activation, hence different temperature co- efficients. The beta degradation leading to the chain breakdown is very sensitive. At high temperatures it is quite important - at low temperatures it becomes very much less. The straight ester hydrolysis perhaps has an intermediate temperature co• efficient and the reaction leading to viscosity increases (perhaps transesterification) must have a lower energy of activation because it does not speed up so much as the others if the temperature is raised.

456 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS At higher temperatures, therefore, other reactions affect a higher proportion of the molecules, and the effects are lost. MR. A. FOSTER: I notice you do not mention trying triethanolamine as a possible reactant. Can you comment? TI•. L•.CT•JR•.R: It does not react. It is necessary to have sufficiently widely spaced reactive groups-and the hydroxyl groups in triethanolamine would not be sufficiently far apart. Even the butane diol for some reason interferes with the reaction rather than reacting itself, which is quite an interesting point. It is mentioned that we did try diamines where the two amino groups were closer together than in the 1:6, and we found that the 1:4 diamine reacted as opposed to the interference by the 1:4 diol. The 1:3 diamine also reacts in this way but in spite of claims in a patent (4) we can not make ethylene diamine work. The original patent (4) referred to the forma- tion of an insoluble product by reaction of propylene glycol alginate and ethylene diamine present together in a film, and it is very difficult to say whether, in these conditions, the amine is reacting or whether it is simply an effect of the alkali on the propylene glycol alginate. DR. F. J. WEYMO•J•I•: You have given us some information concerning the effect of propylene glycol alginate on starches and polyvinyl alcohol. Have you any- thing to say about the effects with cellulose ethers? TI•. L•c•uR•R: It does give a gelling effect with carboxymethyl cellulose, and also with other cellulose ethers but not very strongly. We have not looked at them very thoroughly and we paid more attention to substances that showed greater effects, in particular starch and polyvinyl alcohol. MR. C. PuGI•: It seems to me that the fact that it is necessary to have a fairly high minimum concentration before you change from hydrolysis to cross-linking must have some influence on the theory involved. Would you care to comment any more on this aspect? TI•. L•.c•uR•-R: I think the hydrolysis reaction is probably going on at the same rate all the time and you get the effect of increase of viscosity only if conditions are suitable for the cross-linking reaction to take place faster than the hydrolysis. If we have some reaction in which, say, a hydroxyl group in the propylene glycol alginate goes to one of the ester groups, it is fairly reasonable to suppose that as the concentra- tion is increased the probability of this reaction increases quite steeply. MR. J. J. H¾•)•.-SMITI•: You say in page 455 that the PGA-starch product is broken down by enzymes. Would you like to comment on this, compared with the normal stabilising of starch solutions against enzymic breakdown by PGA? TI• L•.CTUR•R: This stabilising action is effective only over the pH range of 3-4.5, a range in which amylyric enzymes do not normally function. I see you do not quite agree with that and perhaps I should say that it is a less important range in digestive processes. We have checked the claims of the patent (8) and agree that inhibition takes place in the stated range, but not appreciably at high pH values. Digestion of starch normally starts with the action of amylase in the saliva, and at the pH to be expected in the mouth there is no inhibiting effect from PGA. On the question of enzymic breakdoxvn, it is rather interesting that the gelatine- (8) U.S. Pat. 3 332 786: Method of preparing enzyme stable starch and product.