Green Chemistry Blog

Polymer scientists from Aachen, Germany, have developed a novel and green method to produce biocompatible polyesters using Novozyme 435 as the catalyst.

The polyester poly(pentadecalactone) (PPDL) investigated in this work is a non-toxic, highly crystalline and hydrophobic material – similar to polyethylene. By copolymerizing pentadecalactone with functional e-caprolactones and macrolactones containing C=C double bonds, epoxide rings and amide functionalities, it was found that the properties of PPDL could be tuned and crystallinity was reduced – increasing the biocompatibility of the material which is necessary for applications in drug-delivery devices or scaffolds.

Using the Novozyme 435 enzyme catalyst, copolymerization of PDL with two 7-membered lactones leads to a near quantitative monomer conversion.

To find out more, click the link below to read the Green Chemistry article in full – free to access until 21st March 2011.

Tailor-made polyesters based on pentadecalactone via enzymatic catalysis by C. Vaida, H. Keul and M. Moeller
DOI: 10.1039/C1GC15044H

Scientists from the Netherlands and the UK have conducted a solvent screening study aimed at identifying greener alternatives for the commonly used solvent dichloromethane in N-oxy catalysed bleach oxidations of various alcohol substrates.

The team found that environmentally acceptable ester solvents, notably isopropyl acetate and methyl acetate, gave results comparable to or better than dichloromethane.

However, there was no apparent correlation between common solvent properties and performance.

A comparison of two co-catalysts, NaBr and borax, revealed that borax gave better results with cinnamyl alcohols whereas NaBr was generally better with the other alcohols.

The team also studied the effect of catalyst loading. In the oxidation of 3-phenyl-1-propanol the amount of N-oxy catalyst could be effectively reduced to a mere 0.1 mol%.

They concluded that due to the complex nature of these systems, there is not a single set of conditions that gives good results for all alcohols. However, by employing a simple screening approach to assess solvent, catalyst and co-catalyst combinations, similar or even better results can often be achieved in solvents other than dichloromethane.

Read more about this article:

Towards greener solvents for the bleach oxidation of alcohols catalysed by stable N-oxy radicals
M H A Janssen, J F Chesa Castellana, H Jackman, P J Dunn and R A Sheldon, Green Chem., 2011, DOI:10.1039/c0gc00684j

Philip Jessop and co-workers report tertiary amine solvents with switchable-hydrophilicity which have been applied to recycling polystyrene foam.

These switchable-hydrophilicity solvents (SHS) have very low miscibility with water and air, but are completely miscible in the presence of a CO₂ atmosphere.  Jessop and his team had previously reported using N,N,N’-tributylpentanamidine as a SHS which could easily be removed from organic products.  However, N,N,N’-tributylpentanamidine is very difficult to synthesise and is not commercially available.

In this work, Jessop reports the use of several tertiary amines which are either commercially available or easily prepared.  As well as investigating the factors which affect the rate of switching, the group also applied one of the amines studied to the recycling of polystyrene foam.  The polystyrene foam was dissolved in one of the SHSs, and after addition of carbonated water formed dense polystyrene.  In future, this could potentially make the transportation and recycling of polystyrene foam waste less energy intensive and more efficient.

Access this article for free by clicking on the link below:

Tertiary amine solvents having switchable hydrophilicity

Philip G. Jessop, Lisa Kozycz, Zahra Ghoshouni Rahami, Dylan Schoenmakers, Alaina R. Boyd, Dominik Wechsler and Amy M. Holland, Green Chem., 2011, DOI: 10.1039/C0GC00806K

For a related article, please see:

A solvent having switchable hydrophilicity
Philip G. Jessop, Lam Phan, Andrew Carrier, Shona Robinson, Christoph J. Dürr and Jitendra R. Harjani, Green Chem., 2010, 12, 809-814
DOI: 10.1039/B926885E

Beckman and Munshi reports a reversible CO₂ carrier (RCC) for the carboxylation of ketone to β-ketoester under ambient CO₂ pressure and temperature.

RCC has been synthesized by immobilizing 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) on methylhydrosiloxane support and reacting with CO₂ with 100% degree of functionalisation. RCC is found to be recyclable and shows retention of activity in 5 recycles. CO₂ absorption under ambient temperature and desorption at 120 °C renders the material suitable for carrying out carboxylation reactions at 25 °C with excellent yields. The yield of the reaction can reach up to 100% with TON 200 in 4 h. The extent of the reaction primarily depends upon enol content of the substrate. β-Ketoacid produced during the reaction can be isolated and converted to its corresponding methyl ester derivative by reacting with methyl iodide.

Access this article for free by clicking on the link below: 

Ambient carboxylation on a supported reversible CO₂ carrier: ketone to β-keto ester, Eric J. Beckman and Pradip Munshi, Green Chem., 2011, DOI: 10.1039/C0GC00704H, Advanced Article, Paper

Righi and co-workers here present the life cycle assessment (LCA) of cellulose dissolution with ionic liquids 1-butyl-3-methylimidazolium chloride (Bmim Cl). The authors compared the “greenness” of the process with the well established environmental friendly N-methyl-morpholine-N-oxide (NMMO)/H2O process. Results from the LCA suggest that both processes are comparable.

Specifically, the process with Bmim Cl generates a higher environmental load on abiotic resource depletion, emissions of volatile organic compounds and ecotoxicity than the NMMO/H2O process. Conversely it has some environmental advantages with regards to human toxicity. In both cellulose dissolution processes, the major contributions to the environmental impacts come from precursor syntheses.

Read more about this article here:

Comparative cradle-to-gate life cycle assessments of cellulose dissolution with 1-butyl-3-methylimidazolium chloride and N-methyl-morpholine-N-oxide

Serena Righi, Andrea Morfino, Paola Galletti, Chiara Samorì, Alessandro Tugnoli and Carlo Stramigioli
Green Chem., 2011, DOI: 10.1039/C0GC00647E, Paper