Depolymerising hemicellulose into platform sugar molecules is a key step in developing the concept of an integrated biorefinery. This reaction is traditionally catalysed by either enzymes or homogeneous mineral acids. We compared various solid catalysts for hemicellulose hydrolysis, running reactions in water, under neutral pH and relatively mild temperature and pressure (120 °C and 10 bar) conditions. Sulphonated resins are highly active, but they leach out sulphonic groups. Sulphonated silicas are less active, but more stable. They have weakly and strongly bound sites and the strongly bound ones do not leach. Zeolites are moderately active and stable. Among them, H-ferrierite especially, despite its small pores, exhibited high activity as well as good recyclability

The anoxic, alkaline hydrolysis of cellulosic materials generates a range of cellulose degradation products (CDP) including α and β forms of isosaccharinic acid (ISA) and is expected to occur in radioactive waste disposal sites receiving intermediate level radioactive wastes. The generation of ISA's is of particular relevance to the disposal of these wastes since they are able to form complexes with radioelements such as Pu enhancing their migration. This study demonstrates that microbial communities present in near-surface anoxic sediments are able to degrade CDP including both forms of ISA via iron reduction, sulphate reduction and methanogenesis, without any prior exposure to these substrates. No significant difference (n = 6, p = 0.118) in α and β ISA degradation rates were seen under either iron reducing, sulphate reducing or methanogenic conditions, giving an overall mean degradation rate of 4.7×10−2 hr−1 (SE±2.9×10−3). These results suggest that a radioactive waste disposal site is likely to be colonised by organisms able to degrade CDP and associated ISA's during the construction and operational phase of the facility.

l-Proline is grafted onto silica (MCM-41) in a single step and shows high activity and enantioselectivity in an aldol reaction.

ABSTRACT:Solid bi-functional acid-base catalysts were prepared in two ways on an amorphous silica support: 1) by grafting mercaptopropyl units (followed by oxidation to propylsulfonic acid) and aminopropyl groups to the silica surface (NH 2 -SiO 2 -SO 3 H), and 2) by grafting only aminopropyl groups and then partially neutralising with phosphotungstic acid, relying on the H 2 PW 12 O 40 -ion for surface acidity (NH 2 -SiO 2 -NH 3 + [H 2 PW 12 O 40 -], denoted as NH 2 -SiO 2 -PTA).Surface acidity and basicity were characterised by adsorption calorimetry, using SO 2 as a probe for surface basicity and NH 3 for surface acidity. Catalytic activities were compared in a two-stage cascade: an acid-catalysed deacetalisation followed directly by a base-catalysed Henry reaction. Overall, the NH 2 -SiO 2 -SO 3 H catalysts showed higher concentrations and strengths of both acid and base sites, and higher activities than NH 2 -SiO 2 -PTA. Both catalysts showed evidence of cooperative acid-base catalysis. Importantly, the bi-functional catalysts exhibited catalytic advantage over physical mixtures of singly functionalised catalysts. 3 INTRODUCTIONMany liquid phase processes in fine chemicals synthesis require acid or base catalysts. Conventionally, homogeneous acids and bases dissolved in the reaction mixtures are used. In most cases, replacing these with solid acids and bases brings substantial environmental benefit by reducing waste and simplifying product separation. 1-3Almost inevitably, however, solid acids and bases are less active than their homogeneous counterparts. Despite this, one case where they might be able to offer particular advantage is where both acid and base catalysis is required, either in sequential steps or through a cooperative catalytic mechanism. A difficulty associated with preparation of the aminopropyl/propylsulfonic acid bi-functional catalysts (NH 2 -SiO 2 -SO 3 H) is that the acid group is grafted to the silica using (3-mercaptopropyl)trimethoxysilane (MPTMS) and an oxidation step is required to convert the thiol (-SH) to sulfonic acid (-SO 3 H). The two main routes reported are based on hydrogen peroxide/sulfuric acid, and on nitric acid (as both oxidant and acidifier). 11,12 The method used must be chosen to effectively oxidise thiol 12 but with minimal reaction with the base groups. Nitric acid has been shown to be the more effective reagent under these conditions 13 so nitric acid is used as the oxidant in the work reported here.An amorphous silica gel has been used as the catalyst support, rather than the ordered SBA-15 silica used in our previous work. Silica gel does not exhibit the friability and low bulk density of SBA-15 14-16 while the surface properties and stability are similar, and it can be functionalised in the same way. The silica gel used here has been chosen to have an average pore diameter similar to that of SBA-15. The tandem deacetalisation-Henry reaction shown in Scheme 2 has been used. The first step is the acid-catalysed deacetalisation of benzaldehyde dimethyl acetal i...

Best practice for scale-down of gas−liquid reactions requires control of the volumetric mass transfer coefficient, k L a. It is demonstrated that the use of small bubble columns can provide well-controlled k L a and catalyst dispersion down to a scale of 3 cm 3 . This scale is several times less than has been previously demonstrated for heterogeneously catalysed reduction using gaseous hydrogen and is more easily reproduced than small scale stirred vessels. Measurements have been made at a fixed total gas flow, with the effective mass transfer rate being adjustable by dilution of the hydrogen flow with either helium or nitrogen. ■ INTRODUCTIONDuring the early stages of chemical process development, the quantity of available starting material often restricts the scale on which development work can be conducted. This can be problematical in the case of gas−liquid reactions, in particular hydrogenation, where selectivity is often sensitive to the solution concentration of hydrogen and consequently to the relative rates of reaction and mass transfer. In these cases control of the volumetric mass transfer coefficient, k L a, is necessary to ensure that laboratory experimentation can properly simulate the processing conditions expected on the manufacturing scale. There are many examples of the sensitivity of hydrogenation processes to operating conditions. Sun et al. 1 first pointed out the interplay between hydrogen pressure, the volumetric mass transfer coefficient and the intrinsic chemical kinetics in determining the rate of a hydrogenation process and further pointed out that, in the case of parallel competing processes, relative rates and hence selectivities could be a function of these three variables. A range of examples confirms the generality of this principle with respect to olefin and ketone hydrogenation. 2−4 Merck workers also encountered the effect in the catalytic hydrogenation of an imine, in which some defluorination of an aryl fluoride occurred under "hydrogen starved" conditions, 5 and were able to devise satisfactory manufacturing conditions based on a knowledge of the volumetric mass transfer coefficient under operating conditions. In the hydro-dechlorination of a benzyl chloride, dimerization instead of reduction occurred under hydrogen starved conditions. 6 Hydrogen starvation is implicated in problems with the reduction of nitro compounds, where azo and azoxy byproducts can be formed, 7 and where leaching of metal from the catalyst support can occur. 8 Reduction of nitriles is extremely sensitive to the processing conditions, and formation of secondary 9 and tertiary amines via trapping of the intermediate imines with the first-formed primary amine is well-known, and avoidance of hydrogen starvation is one component of strategies used to achieve a good yield of primary amine products. 10 As a consequence of these considerations, it is now accepted in major pharma and agrochemical companies that "best practice" in the design and scale-up of hydrogenation processes using molecular hydrogen (as op...

Route design and process development of the small nitrogen heterocycle 2·HCl, a constituent of AZD5718 (1), is described. The novel synthetic sequence to 2.HCl involves a desymmetrizing alkylation of 4-nitropyrazole, a non-cryogenic lithiation-alkoxycarbonylation, and a global reduction-cyclization. This new synthetic route was implemented in the manufacture of 2.HCl and was able to deliver over 1000 kg of product with a yield of 77% over the three stages.

To ensure compliance with regulations regarding levels of residual metals in pharmaceutical products, process research and development (PR&D) in the pharmaceutical industry makes wide use of metal scavengers characterized by high selectivity and effective removal ability. Thiol homogeneous scavengers are notably effective in terms of eliminating palladium from intermediates and active pharmaceutical ingredients (APIs) during production. The strategies for detecting residual thiol homogeneous scavengers such as N-acetylcysteine are presently problematic within pharmaceutical analysis. Herein a simple and effective method using inductively coupled plasma-mass spectrometry (ICP-MS) for the simultaneous detection of N-acetylcysteine (based on sulfur determination) and palladium is described. The method was successfully validated with regard to linearity, accuracy, repeatability, the limit of quantification (LOQ), and the limit of detection (LOD).