Leo Ernest Manzer

An overview of the commercial development of chlorofluorocarbon (CFC) alternatives

Abstract Chlorofluorocarbons (CFCs) are now believed to be major contributors to the seasonal ozone depletion over the Antarctic continent. They are so important to many aspects of modern society, that substitutes must be rapidly found and commercialized. The identification of suitable substitutes is difficult when issues such as toxicity, flammability, cost, environmental impact and physical properties are considered. Several candidates, azeotropes and blends which meet these criteria, have been selected by the industry and significant research and development programs are underway to commercialize them. Unlike the simple, fully-halogenated CFCs which can only be made in a single step, there are many potentially viable routes to the alternatives, requiring significant improvements in catalysis. Many other important issues such as toxicity, environmental impact, materials compatibility, energy efficiency, developing country needs and product life cycle of the alternatives need to be resolved before a timely transition to substitutes can be accomplished on a global scale.

Improved syntheses of chlorodicyclopentadienyl derivatives of scandium(III), titanium(III) and vanadium(III)

Abstract An improved synthesis of chlorodicyclopentadienyl derivatives of scandium(III), titanium(III) and vanadium(III) has been developed by the reaction of thallium cyclopentadienide with the appropriate anhydrous metal trihalides.

Polypyrazolylborate complexes of titanium and vanadium

Abstract A series of polypyrazolylborate complexes of the type Cp 2 Ti(Pz 4− x BH x ) (where x is 0, 1, or 2; Pz is pyrazole or substituted pyrazole) have been prepared. Electron spin resonance and electronic spectroscopy indicate that the cyclopentadienyl groups are pentahapto and the pyrazolylborate ligand is bidentate. The reaction between Cp 2 VCl and KHBPz 3 gave a mixture of compounds from which the vanadium(II) compound, CpV(HBPz 3 ), was isolated. KHBPz 3 reacts with MCl 3 (THF) 3 (where M = Ti, V) to give MCl 2 (THF)(HBPz 3 ) as paramagnetic air sensitive cyrstalline solids. Cyclopentadienyltitanium trichloride reacts with KHBPz 3 to give Cp(HBPz 3 )TiCl 2 as a deep red crystalline solid. Reduction of this compound with zinc gave Cp(HBPz 3 )TiCl which can also be prepared from [CpTiCl 2 ] x and KHBPz 3 .

A new chelated C,N-benzyllithium reagent and some organometallic derivatives of selected early transition metals

Abstract The reactions of LiCH 2 C 6 H 4 - o -NMe 2 with Cp 2 MCl (M = Ti, V; Cp = η 5 -C 5 H 5 ), CpTiCl 2 , CrCl 3 , and ScCl 3 have led to the isolation of thermally stable, air-sensitive organometallic complexes whose stability is attributed to chelation. The reaction of Cr(CH 2 C 6 H 4 - o -NMe 2 ) 3 with CO 2 gives a paramagnetic complex in which CO 2 has inserted into only one CrC bond and with diketones to give (diketonate)Cr(CH 2 C 6 H 4 - o -NMe 2 ) 2 .

Syntheses and structures of novel paramagnetic organometallic complexes of manganese(II) and chromium(II)

Abstract The reactions of LiC6H4CH2NMe2 with MnI2 and CrCl2 in tetrahydrofuran gave the air-sensitive, paramagnetic complexes Li2(THF)2MX2(C6H4CH2NMe2)2. The solvated lithium halide may be removed from these complexes to give M(C6H4CH2NMe2)2 as paramagnetic organometallic complexes. Similarly the reactions of LiCH2C6H4NMe2 with CrCl2 and MnI2 gave M(CH2C6H4NMe2)2 whose magnetic moments and molecular weight measurements indicate that association occurs in solution. The X-ray crystal structure of Mn(CH2C6H4NMe2)2 was determined. The molecule is dimeric, containing one bridging and one terminal CH2C6H4NMe2 ligand per metal. The bridging ligand is bonded to both manganese atoms through a common CH2 group. One manganese atom has a bidentate CH2C6H4NMe2 ligand while the other manganese atom has a monodentate o-dimethylaminobenzyl ligand.

Kinetics of the reoxidation of propylene-reduced γ-bismuth molybdate: A TAP reactor study

Abstract The reoxidation of γ-bismuth molybdate following reduction by propylene at elevated temperatures was examined using a TAP reactor. Use of the TAP reactor permitted examination of the catalyst surface at the earliest stages of reaction involving less than 1/100th of the surface. Pulsing of oxygen over the reduced catalyst at high (840 torr) and low (6 × 10 −7 torr) total pressures yielded kinetic information on the reoxidation rates as functions of oxygen partial pressures, oxygen vacancies and temperature. In both pressure regimes, the reoxidation was found to be first order in both oxygen and in oxygen vacancies created during the propylene reduction. At high pressures, the reoxidation activation energy was found to be 3.4 kcal/mol while at low pressures it was measured as 5.0 to 8.7 kcal/mol.

Toward catalysis in the 21st century chemical industry

Abstract The general public is becoming much more concerned over environmental issues, and decisions are being made that are not necessarily based on science. For the chemical industry it is becoming increasingly difficult to obtain permits, eliminate waste, construct incinerators and receive and ship toxic materials. The effect will clearly increase the relative importance of environmental vs. variable costs for current and future plants. As a result, the following will become increasingly important: processes with 100% yield (by whatever process); catalyst recovery, regeneration and recycle; heterogenization of homogeneous catalysts; increasing importance of chiral pharmaceutical and agrichemicals; polymer recycle and environmentally safer processes. Several of these aspects, from DuPont R&D will be highlighted in this paper.

Perclene-based routes to HFC-134a (CF3CH2F): an environmentally friendly replacement for CFC-12

Abstract The reaction of tetrachloroethylene with HF and Cl 2 or HF to either CFC-114a (CF 3 CFCl 2 ) or HCFC-124 (CF 3 CFHCl) represent potential intermediates to HFC-134a, a key replacement for CFC-12 in refrigeration and air-conditioning applications: The initial reaction of perclene with HF over Cr 2 O 3 and AlF 3 -based heterogeneous catalysts to a mixture of HCFC-123 and HCFC-124 has been studied. The selectivity is highly dependent on the method of catalyst preparation. Mechanistic aspects of the perclene hydrofluorination chemistry will be discussed. Conversion of the HCFC- 124 with hydrogen to HFC-134a proceeds smoothly over a variety of catalysts in high selectivity.