It is not gold all that shines, and it is not all green what looks green. Amino acids and proteins hydrolysates surfactants that enjoy a revival in personal care on the back of the “sulphate free” and “ethylene oxide free” hysteria use raw materials and processes that may cast doubts on their real “green” nature. This opens opportunities for a fresh, innovative approach to the acyl halides chemistry that has hitherto been the only synthetic route for their production.

INTRODUCTION

Sometimes, looking at the evolution of the surfactants industry I cannot avoid the feeling of being a middle age alchemist, propelled in the third millennium by the effect of mysterious phenomena caused by space-time warping.

When I stopped taking mother’s milk and started to mess with colloid chemistry life was simple and easy. Take for example personal care: for surfactants HLB was the name of the game. It was at the same time the reference point and the lulling tool to solve emulsification and dispersion problems and to provide guidance to identify the optimum surfactants or their combinations to deliver the desired effects.

But now life has evolved into a much more sophisticated environment: microbiotics, nutritional chemistry, vibrational cosmetics just to quote a few. And what about surfactants? Well, just make sure they are sulphate-free (possibly), ethylene oxide-free (possibly), natural/renewable/sustainable (possibly).

In this context I firmly believe that alchemy has still a lot to say. Just follow me.

RETHINKING WASTE

GUIDO BOGNOLO

WSA Associates | Belgium

BETTINA KÖNIG

SGS INSTUTUT FRESENIUS Austria GmbH

Germany & Austria

Bio...

REFERENCES

In the golden age of surfactants, between the 1930ties and 1940ties when empiricism was reigning and regulatory just an entry in dictionaries there was an amazing production of surface active molecules. Some grew to multi million tons markets, some remained at the level of laboratory curiosities, some happened to be in the wrong place at the wrong time. But they did not disappear.

In the early 1930ties innovative scientists in I.G. Farben used the Schotten-Baumann reaction (first reported in 1883) to produce protein hydrolysates and amino acid surfactants, among others acyl taurates and acyl sarcosinates. These surfactants enjoyed commercial success at the time and for years thereafter, before being dwarfed by the alkyl benzene sulphonates, the alkyl and alkyl ether sulphates, the ethoxylated nonionics and many more. But now, at least in personal care, they are surfacing again on the back of the drivers mentioned above.

The acylation chemistry has been instrumental in enabling the renaissance of what are viewed now as shining examples of the “green” concept, and that as such are eyed quite favourably by the personal care industry against the much hated (yet quite cost/effective) petrochemicals.

But I am left with an unpleasant feeling. Are we talking of really green products? Just consider a taurate: on paper the raw materials needed for production are fatty acid chlorides and N-methyl taurine. And fatty acid chlorides are just derived from natural fatty acids and N-methyl taurine is an amino acid found in nature, are they not?

Now let be factual, dispassionate, and logical for a moment.

ZERO WASTE BEAUTY

Today the most practiced route to fatty acids is the hydrogenation of methyl esters obtained from the methanolysis of triglycerides. Even if methanol is recycled some losses are unavoidable. And methanol is not really green.

Then the fatty acid has to be cleaned and converted into the chloride, which is performed by sulfochlorination with SOCl₂ (thionyl chloride) and that leaves behind waste hydrochloric acid that has to be disposed off. And SOCl₂ is the reaction product of Sulphur trioxide and Sulphur dichloride. Not really green chemistry. Alternatively, one can use the PCl₃ (or PCl₅ or OPCl₃) route or even the COCl₂(phosgene) route. Surprisingly, some of the organisations that make a living out of green certification accept the phosgene route but ban the PCl₃ route. It may be an emotional reaction, but I feel confused (and worried).

And what about N-methyl taurine? Surely it is an amino acid found in nature, but the volumes demanded by the commercial applications have to be produced synthetically by, for example, the addition of methylamine to 2-chloroethane sulphonic acid or to vinyl sulphonate in aqueous solution. At the risk of being pedantic, once more not really green chemistry. If I may open a parenthesis here other synthetic amino acids used to make surface active agents rely on the hydrogen cyanide Strecker process (dating back to 1850).

Finally, the fatty acid chlorides are reacted with N-methyl taurine producing HCl waste that has to be neutralized and disposed off.

CONSUMER PERCEPTIONS

In my naivety I cannot avoid the feeling that surfactants from amino acid and protein hydrolysates may be portrayed as green, but that the production process and the raw materials used are surely anything but green.

Then my question: is it conceivable to make the acylation chemistry really green? If not in full, at least greener (and maybe economically more attractive) than it is today?

One idea is perhaps to rely on nature instead of chemistry. For example, why not use enzymes to do the job of the fatty acyl chlorides and convert directly fatty acids and amino acids into surfactants? After all, amides linkages of amino acids are at the basis of any proteic synthesis. I have been told that my thinking is not original, that it has been already tried and that it has failed because of unfavourable kinetics, unacceptable for industrial scale production.

But was it tried really hard? If the thermodynamics of the process are OK (which seems to be the case) does it look sensible to surrender in front of the kinetic challenge? Similar situations have occurred innumerable times in the past and in any field. If the challenges would not have been taken after the initial failures, we would not enjoy the standards of living we have today.

And allow me to be provocative: there is space for real innovation here! At least for those who do not pay to innovation just lip service.