Alexander R. Mitchell

A review of energetic materials synthesis

Energetic materials (explosives, propellants and pyrotechnics) are used extensively for both civilian and military applications. There are ongoing research programs worldwide to develop pyrotechnics with reduced smoke and new explosives and propellants with higher performance or enhanced insensitivity to thermal or shock insults. In recent years, the synthesis of energetic, heterocyclic compounds have received a great amount of interest. Heterocycles generally have a higher heat of formation, density, and oxygen balance than their carbocyclic analogues. This review will concentrate on recent advances in the synthesis of heterocycles as energetic materials and will complement the excellent review of recent advances in energetic materials published in 1998 by Agrawal [Prog. Energy Combust. Sci. 24 (1998) 1].

Direct photometric or fluorometric assay of proteinases using substrates containing 7-amino-4-trifluoromethylcoumarin

N-Acyl derivatives of 7-amino-4-trifluoromethylcoumarin (I) provide new and novel substrates for the assay of proteinases, allowing either direct fluorometric or photometric measurements. The yellow-green fluorescence of the free coumarin I makes it possible to visually observe hydrolysis of the arylamide bond, thus making it a very useful non-mutagenic fluorophore for the identification and quantification of proteinases whether in dynamic assay or in intact cells.

Synthesis of proteins by native chemical ligation using Fmoc-based chemistry.

C-terminal peptide alpha-thioesters are valuable intermediates in the synthesis/semisynthesis of proteins by native chemical ligation. They are prepared either by solid-phase peptide synthesis (SPPS) or biosynthetically by protein splicing techniques. The present paper reviews the different methods available for the chemical synthesis of peptide alpha-thioesters using Fmoc-based SPPS.

PREPARATION OF AMINOMETHYL‐POLYSTYRENE RESIN BY DIRECT AMIDOMETHYLATION

Zur Herstellung von Aminomethyl-polystyrolen (IV) wird die Tscherniac-Einhorn- Reaktion herangezogen, nach der das Polystyrol mit Hydroxymethyl- oder mit Chlormethylphthalimid (IIa) und (IIb) zu (III) kondensiert wird.

Advances in the chemical conversion of surplus energetic materials to higher value products

The demilitarization of nuclear and conventional munitions in Russia and the West is producing millions of pounds of surplus energetic materials. Historically, energetic materials (high explosives, propellants, and pyrotechnics) have been disposed by open burning/open detonation (OB/OD). The use of OB/OD is becoming unacceptable due to public concerns and increasingly stringent environmental regulations. Our goal is to develop environmentally sound and cost-effective alternatives to OB/OD. We have investigated the use of recycled high explosives as raw materials for producing a variety of higher value products. In this paper, we review chemical conversion activities with an emphasis on recent work from Lawrence Livermore National Laboratory (LLNL).

Bruce Merrifield and solid-phase peptide synthesis: A historical assessment†

Bruce Merrifield, trained as a biochemist, had to address three major challenges related to the development and acceptance of solid‐phase peptide synthesis (SPPS). The challenges were (1) to reduce the concept of peptide synthesis on a insoluble support to practice, (2) overcome the resistance of synthetic chemists to this novel approach, and (3) establish that a biochemist had the scientific credentials to effect the proposed revolutionary change in chemical synthesis. How these challenges were met is discussed in this article.

The solubility and recrystallization of 1,3,5-triamino-2,4,6-trinitrobenzene in a 3-ethyl-1-methylimidazolium acetate–DMSO co-solvent system

Ionic liquids have previously been shown to dissolve strong inter- and intramolecular hydrogen-bonded solids, including natural fibers. Much of this solubility is attributed to the anions in ionic liquids, which can disrupt hydrogen bonding. We have studied the solubility and recrystallization of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a very strong inter- and intramolecular hydrogen-bonded solid, in various ionic liquid solvent systems. We discovered that acetate-based ionic liquids were the best solvents for dissolving TATB, while other anions, such as Cl−, HSO4− and NO3− showed moderate improvements in the solubility compared to conventional organic solvents. Ionic liquid–DMSO co-solvent systems were also investigated for dissolving and recrystallizing TATB.

Comparison of New and Legacy TATBs

Two newly synthesized versions of the insensitive high explosive (IHE) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) were compared to two legacy explosives currently used by the Department of Energy. Except for thermal analysis, small-scale safety tests could not distinguish between the different synthetic routes. Morphologies of new TATBs were less faceted and more spherical. The particle size distribution of one new material was similar to legacy TATBs, but the other was very fine. Densities and submicron structure of the new TATBs were also significantly different from the legacy explosives and the densities of pressed pellets were lower. Recrystallization of both new TATBs from sulfolane produced nearly hexagonal platelets with improved density and thermal stability.

Studies in Solid Phase Peptide Synthesis: A Personal Perspective

By the early 1970s it had became apparent that the solid‐phase synthesis of ribonuclease A could not be generalized. Consequently, virtually every aspect of solid‐phase peptide synthesis (SPPS) was reexamined and improved during the decade of the 1970s. The sensitive detection and elimination of possible side reactions (amino acid insertion, Nα‐trifluoroacetylation, Nαϵ‐alkylation) were examined. The quantitation of coupling efficiency in SPPS as a function of chain length was studied. A new and improved support for SPPS, the “PAM‐resin,” was prepared and evaluated. These and many other studies from the Merrifield laboratory and elsewhere increased the general acceptance of SPPS leading to the 1984 Nobel Prize in Chemistry for Bruce Merrifield.