Biological Feedback from Steve Jones, Interview by DBSW
by David Bradley
British geneticist Steve Jones wants to make the arguments contained in Darwin's evolutionary text as accessible as possible to modern audiences, and succeeds with the delightful Darwin's Ghost. He hangs his own words on Darwin's scaffold to bring evolution up-to-date - it is amazing how much has changed in a century, and how little. You can read about Professor Jones' life and times in the Elemental Discoveries interview in which he reveals the juvenile and embarrassing fascination that first got him into biology.
No solvent is needed for the aldol reaction, according to Australian
chemists, if the solid starting materials are simply ground together with sodium
hydroxideas a catalyst.
Aldol reactions are widely used in synthetic chemistry. Simply react a carbonyl compound with an electrophile to yield a beta-hydroxycarbonyl compound, dehydrate the product to an alpha-beta-unsaturated carbonyl compound and you have the starting point for agrochemicals and pharmaceuticals.
According to Colin Raston and Janet Scott of Monash University, Melbourne, most aldol reactions require organic solvents to work and are inefficient produce lots of waste solvent.
The researchers figured that the reactivity of the starting materials themselves might be enough even at room temperature in the solid state, if they could kick start the reaction with solid sodium hydroxide. The researchers have found that the simple action of grinding the materials together with the catalyst will indeed make them react. Their approach means they can avoid the need for a noxious solvent in the preparative reaction steps and only produce a small amount of acidic aqueous waste.
Raston and Scott point out that the big advantage, aside from avoiding solvent, is that in solution the reaction would normally yield a range of products, with virtually no selectivity. This can be overcome with a preforming step in which the enolate intermediate is selected out for the next step but by using solids in the appropriate molar proportions the desired product only is obtained.
The Monash team demonstrated the approach using veratraldehyde, 4-phenylcyclohexanone and 1-indanone in various combinations to produce a selection of aldol condensation products. The product of the reaction of veratraldehyde and 1-indanone is a single compound while veratraldehyde and 4-phenylcyclohexanone can lead to one of two useful products - a mono and a bis adduct.
It doesn't matter what order the reactants are added except that if the carbonyl-containing reagents are ground together before adding the NaOH a viscous, sticky liquid is produced. This the researchers say hints at the underlying mechanism of the reaction as the reaction mixture must be a solution of the carbonyl compounds in each other reacting to form a solid product which separates from this solution as reaction proceeds. The NaOH hides this liquid phase by speeding the process up. 'We believe this approach is likely to become popular in industry for the clean tech aspects, and for the reason that the paste can be stored for long periods,' adds Raston.
C. Raston et al., Green Chemistry - DOI: 10.1039/a907688c
By supporting the starting materials on a polymer base, UK chemists have
found a way to synthesise azo dyes cleanly and efficiently without the need for
the usual difficult cleanup of hazardous waste products.
Azo dyes are among the most commonly used bulk pigments in countless areas of manufacture, such as textiles, cosmetics and reprographics, and they also find use in chemical analysis and in bacteriological work. They are generally synthesised by diazotisation of an aromatic primary amine and the coupling of the resulting diazonium salt with a phenol or another aromatic amine. Their colourful production, however, is plagued by the fact that this conventional wet-chemistry approach to their synthesis produces vast quantities of toxic and highly coloured downstream waste, which represent a serious disposal problem.
Ian Baxendale and Steven Ley of the University of Cambridge working with Marina Caldarelli of Pharmacia & Uphohn in Milan, have now applied some of the technology of combinatorial chemistry to clean up the synthesis of azo dyes.
By attaching a nitrite to a polymer bead they can produce various diazonium salts by reacting the compound on the beads with a selection of anilines. Solid polymer supports are used to carry the reagents so that products can be readily filtered off and the supports removed without the need for standard work-up processes and solvent-based separation and purification methods.
The process might not only be exploited to reduce waste from azo dye production but could also be applied to robotic combinatorial production of the dyes for selection for new colour characteristics.
S. V. Ley et al., Green Chemistry - DOI: 10.1039/a907688c