Here comes the sun

Keeping safe in the sun is not only good sense, it's big business. Since the links between exposure to sunlight and skin cancer have been more widely researched and publicised, demand for effective suncreens has grown rapidly.

However, ultraviolet absorbers are complex molecules, and tend to be expensive to synthesise and purify. BASF's laboratories, which work around a similar integrated 'Verbund' system to the rest of the company, have proved an effective resource for finding unexpected ways to make these compounds.

One example of this is Uvinul MC-80. This is the trade name for ethylhexyl cinnamate, an ester of cinnamic acid, which absorbs UV-B radiation. BASF has supplied the raw materials to manufacture cinnamates for some years, but had not produced the final product itself because the process would have been uneconomic. However, collaborations between chemists and process engineers provided the key to reducing the cost of the process.

Michael Hüllmann, a BASF chemist, designed the synthesis while working on reactions involving ketenes. In an adjacent lab, colleagues were working on cinnamate synthesis, and Hüllmann realised that ketenes could be the key to producing cinnamates cheaply. The crucial reaction here would be to insert a ketene into anisaldehyde acetal.

The process design was handled by Christof Kandzia, who integrated the various parts of the synthesis. The anisaldehyde acetal is made by an electrosynthetic process, involving the oxidation of p-cresol. This is done at the anode of an electrical cell, rather than by using metal salts, and therefore produces less waste. The electrosynthesis produces the acetal which is 'trapped' in methanol.

The ketene group is then inserted into the intermediate, using a proprietary catalytic step. The purification process to recover the Uvinul product uses a divided-wall distillation column, which reproduces the effect of multiple distillation columns while using much less energy.

The plant is extremely efficient, Kadzia says, and produces much less waste than a conventional cinnamate plant. This is because the 'classic' synthesis starts from an aldehyde and an organic acetate, and requires equimolar amounts of a base for the reaction to proceed. This produces large quantities of salts in the waste water. The new BASF process avoids the generation of salts, Kadzia says. The plant, which came on-stream early this year, has a capacity of 4500tonnes of cinnamate per year and cost 'tens of millions' of Deutschmarks, according to BASF.

The personal care division of BASF is a major consumer of speciality chemicals, many of them devised for applications far away from this area and put to uses which, sometimes unexpectedly, prove to be particularly demanding.

Take hairspray, for example. What's needed is a polymer that's sticky when wet, but not so sticky that it causes hairs to clump together; rigid enough to set hair in position, but not so rigid that it stops the hair moving altogether; and, of course, environmentally friendly, with no need for ozone-depleting aerosol propellants or volatile organic solvents.

It was the latter that was the biggest problem for BASF labs. In conventional hairsprays, the active ingredients - setting polymers, additives and perfume oils - comprise only 5 per cent of the contents of a can, with the remainder made up of solvent and propellant.

The answer has turned out to be a polyurethane - one which was originally developed for sporting goods. Luviset can be found in skiboots, foam cushions, and skateboard wheels. But these elastic, cushioning properties are also exactly what's needed in hairsprays.

The structure of the polymer also worked in BASF's favour. 'Poyurethanes have a modular structure, so we can vary the starting materials in various ways and specfically adjust the properties of the product,' explains polymer chemist Claudia Wood. In the case of Luviset, the polymer contains a series of building blocks which give the set substance its hardness, while others confer its elasticity.

These are arranged in a way similar to rigid rods connected by springs. When the polymer dries on the hair, this gives hold and support, particularly to curled hair which would otherwise tend to straighten, but still allows the hair to follow the movement of the head.

Luviset also has the advantage of mixing easily with water. This ensures that the drops remain small when it is sprayed from the can - in less water-compatible solvents, the drops tend to enlarge, which limits the effectiveness of the product as it makes it viscous and sticky to the touch. Moreover, the reduced amount of solvent needed makes the product easier and cheaper to formulate.