Mark Andrew Harmer

Solid acid catalysis using ion-exchange resins

In this review article, we describe the use of commercially available polymeric ion-exchange resins for a range of industrially important transformations. Recent developments both on the materials design and applications will be described. Examples of high catalytic activity will be described in areas ranging from alkylation, transalkylation, isomerization, oligomerization, acylation, esterification and nitration. The two main classes of ion-exchange resins are based upon styrene-based sulfonic acids (Amberlyst® and Dow type resins), which show very high activity in the areas of esterification and etherification, to the perfluorosulfonic acid-based catalysts including the recently developed Nafion® resin/silica nanocomposites. These show very high activity in the area of linear alkyl benzene formation, isomerization, and some select acylation type chemistries. These new types of catalysts (which have been used commercially) are adding to the ever-growing portfolio of highly active solid acid catalysts, which couple both economic and environmental drivers to improve organic transformations within the chemical industry.

Immobilisation of bis(oxazoline)–copper complexes on clays and nanocomposites. Influence of different parameters on activity and selectivity

Bis(oxazoline)–copper complexes, immobilised by electrostatic interactions on Laponite and Nafion/silica nanocomposites, have been tested as catalysts in the cyclopropanation of styrene with ethyl diazoacetate. Several factors play a decisive role in the outcome of the reaction. Firstly, the nature of the solid counterion is important, with perfluorosulfonic solids being the best in this regard. Secondly, the nature of the solvent used has a marked influence as some solvents cause the solid support to modify the stereochemical course of the reaction. Finally, the nature of the chiral ligand is also very important, in particular the strength of its copper complex, in order to avoid the formation of non-chiral catalytic copper centres. This particular effect has been highlighted by using a ligand that is able to give strong complexation, namely an iminobis(oxazoline) ligand, and this leads to the best enantioselectivities being obtained for reactions using electrostatically immobilised catalysts.

Bis(oxazoline)-metal complexes immobilised by electrostatic interactions as heterogeneous catalysts for enantioselective Diels–Alder reactions

Abstract The immobilisation by cationic exchange of complexes of a bis(oxazoline) with Cu(II), Mg(II) and Zn(II) has been studied with two types of anionic solid, a laponite clay and a nafion-silica nanocomposite. The results obtained show that the cationic exchange depends on both the geometry of the complex and the nature of the cation. Whereas the immobilisation of square-planar complexes takes place easily, the situation is not the same for tetrahedral complexes. The solids prepared have been used as catalysts in a benchmark Diels–Alder reaction. These solids are efficient catalysts but the enantioselectivities are low, a fact that is related to the presence of non-chiral catalytic sites and to the nature of both the solid counter-ion and the bis(oxazoline) structure.

Scanning tunneling microscopy of the surface topography and surface etching of nanoscale structures on the high‐temperature superconductors

We report on the use of the scanning tunneling microscope (STM) for etching both single crystal and thin film, YBa2Cu3O7−x. Nanoscale features can be generated with the STM by ablation of atoms rastered by the microscope tip. The etching process can be controlled to remove layers of material which are multiples of the c axis (12 A). Various geometric features have been fabricated ranging from fine lines to square etch pits. The STM has also been used to study the growth mechanism and surface topography of thin films of YBa2Cu3O7−x produced by in situ laser deposition (Jc typically 1×106 A cm−2 at 77 K). Step features equal to the c axis of the material can be readily identified which form pinnacles or chip like morphologies at the surface. These surfaces can also be etched with the STM to reveal a more continuous substructure consistent with the high Jc’s observed.

But-1-ene isomerization over Nafion® resin/silica composite catalyst

But-1-ene isomerization to but-2-enes at 50 °C to near thermodynamic equilibrium is observed over a novel high surface area Nafion® resin/silica composite solid acid catalyst at a mass hourly space velocity (MHSV) of but-1-ene of 2.5 h–1.

Renewably sourced polytrimethylene ether glycol by superacid catalyzed condensation of 1,3-propanediol

In this paper we describe the synthesis of a new 100% renewably sourced polymer, polytrimethylene ether glycol (polyol). This is an alternative to petroleum-sourced polytetramethylene ether glycol (PTMEG) and polypropylene glycol (PPG) and adds to the slowly expanding list of polymers from renewables, such as polylactic acid. The polymer is based upon a renewably sourced monomer, 1,3-propanediol (PDO), which itself has a lower environmental footprint compared to the chemically derived monomer, with both lower amount of green house gas emissions and energy use, during formation. Herein we discuss the development of polymerization conditions to provide polytrimethylene ether glycol with low color and low unsaturated end groups using the superacid tetrafluoroethane sulfonic acid (TFESA, b.p. 212 °C). The initial high color (brown) and high unsaturated impurities of the polymer, has been overcome by careful control of the processing conditions, leading to a new class of 100% renewably-sourced polymers. Preliminary kinetic analyses are also reported.

Synthesis and applications of superacids. 1,1,2,2-Tetrafluoroethanesulfonic acid, supported on silica

In this paper we focus on the synthesis and use of superacids, in particular 1,1,2,2-tetrafluoroethanesulfonic acid(TFESA), and describe how these can be optimized for reactions of key industrial importance. One area of considerable interest is the field of superacid catalysis and, specifically, the development of safer and more cost-effective acid catalysts. We report a new simplified route for preparation of these acids, making these more readily available and opening up a large number of opportunities. Partially fluorinated superacids offer several advantages over the acids commonly used in catalysis (sulfuric, hydrofluoric acid and aluminium chloride): lower loadings, lower reaction temperatures (leading to increased selectivity), fewer by-products, shorter reaction times and higher throughput. TFESA and its longer chain analogs are much less volatile than triflic acid (CF3SO3H). We tested these superacids in several processes (aromatic alkylation, acylation of arenes, isomerization, oligomerization and the Fries rearrangement). These materials are excellent acid catalysts, comparable to triflic acid, and yet easier to handle. We have also prepared supported versions of these catalysts and introduced the ability to recycle.

Nuclear magnetic resonance study of a high-surface-area aluminum phosphate glass and its thermally reversible sol-gel precursor.

A novel reaction, based on sol-gel chemistry using an aluminum alkoxide and phosphoric acid to produce a high-surface-area aluminum phosphate glass, was followed by 27Al and 31P nuclear magnetic resonance (NMR). The gelled portion of the alcoholic solutions could be characterized with solid state 27Al methods. We discovered that the gelation, which is very rapid under normal conditions, can be controlled by the addition of HCl to the solution and that the gelation is thermally reversible in the presence of HCl. The NMR results showed that this modified sol-gel behavior is a result of acid hydrolysis of the Al-O-P bonds, leading to network termination by POH groups and octahedrally solvated Al atoms. Similar local structures persist in the amorphous calcination product. The glass surface contains Al sites with strong quadrupole interaction. These sites could not be detected by conventional 27Al NMR methods but their existence was demonstrated with a static echo experiment. The quadrupole coupling constant was determined with the recently introduced transfer of populations in double resonance (TRAPDOR) method (a 1H/27Al double resonance magic-angle spinning experiment). The TRAPDOR results also showed that these sites, which constitute about 30% of the Al in the glass, carry hydroxyl groups. Characterization of the atomic structure of high-surface AlPO4 is important for its use as catalyst support.

Catalytic reactions using superacids in new types of ionic liquids

We will describe the use of superacids, in particular 1,1,2,2-tetrafluoroethanesulfonic acid (TFESA) and 1,1,2,3,3,3-hexafluoropropanesulfonic acid (HFPSA) in the presence of ionic liquids for improved chemical processing for a range of industrially important chemical reactions. In a number of cases the reaction mixture starts as a single phase, allowing for high reactivity, then separates into two phases upon completion of the reaction. This allows for ease of product separation P. T. Anastas and T. C. Williamson, Green Chemistry: Frontiers in Benign Chemical Syntheses and Processes, Oxford University Press, 1998.

UNIQUE SILANE MODIFIED PERFLUOROSULFONIC ACIDS AS VERSATILE REAGENTS FOR NEW SOLID ACID CATALYSTS

A new versatile reagent, a perfluorosulfonate/trisilanol [(OH) 3 Si(CH 2 ) 3 (CF 2 ) 2 O(CF 2 ) 2 SO 3 - M + ], is synthesized and a series of surface bound strong solid acid catalysts developed which are active for catalyzing a range of reactions, for example alkene isomerization, alkylations and acylations.