Walter Thomas Reichle

Synthesis of anionic clay minerals (mixed metal hydroxides, hydrotalcite)

Abstract A number of approaches to the synthesis of a class of anionic clay minerals (M a 2+ M b 3+ (OH) 2 a +2 b (X − ) 2 b · x H 2 O; M 2+ = Mg, Ni, Co, Zn, Cu, etc.; M 3+ = Al, Cr, Fe, Sc; M 2+ /M 3+ ∼ 1−5; X − = water and base stable anion; x = 0−6) have been sumarized. The most general method involves the mixing of a concentrated, aqueous solution of M 2+ and and M 3+ with aqueous hydroxide-carbonate to yield an amorphous gel followed by crystallization at 60–325°. For a number of these materials, the synthetic latitudes with respect to the nature of M 2+ , M 3+ , the M 2+ /M 3+ ratio, the solution pH and the crystallization temperature has been detailed. The crystallization temperature and time influences the particle size, morphology, surface area and the appearance of foreign phases. The incorporation of various interstitial anions by exchange or synthesis is discussed.

Catalytic reactions by thermally activated, synthetic, anionic clay minerals

The thermal decomposition of a number of anionic clay minerals belonging to the pyroaurites-jogrenite group, such as hydrotalcite (Mg6Al2(OH)16(CO2−3) · 4H2O), results in a product (approximately Mg6Al2O8(OH−)2) which is a fairly strong base (pKa ≤ 35) and a useful catalyst for vapor-phase aldol condensations. Replacement of Mg by Fe, Co, Ni, and Zn, and/or replacement of Al by Fe and Cr also results in isomorphous double hydroxides which, on heat treatment, are catalytically active. A rational method of synthesizing these materials having controlled surface areas has been devised. The effect of the thermal decomposition temperature, MgAl ratio, isomorphous metal cation substitution, and interstitial anion nature on the rate and efficiency of acetone oligomerization has been examined. These materials will also catalyze HD exchange of acetone and toluene but not of n-propylbenzene or cyclohexane (300°C, LHSV ~1). They are relatively poor catalysts for olefin isomerization as well as aromatization of 1,4-cyclohexadiene and limonene.

The nature of the thermal decomposition of a catalytically active anionic clay mineral

Certain synthetic, anionic clays, after a carefully controlled heat activation, have been shown to promote a wide variety of base catalyzed reactions such as aldol condensations, oxirane polymerizations, carbon-bound HD exchange, and lactone polymerizations. The changes which take place during the heat activation of such a synthetic, anionic clay mineral, hydrotalcite (Mg6Al6(OH)16 (CO3 · 4H2O), have been studied by 27Al nuclear magnetic resonance-magic angle spinning, Auger and XPS spectroscopy, transmission electron microscopy, and high resolution nitrogen desorption techniques. The heating of this material (to ~450 °C) results in the loss of interstitial water, carbon dioxide, and dehydroxylation until a catalytically active material analyzing approximately as Mg6 Al2O8(OH)2 remains. This heating does not cause a change in the crystal morphology nor in exfoliation of the layered structure. Instead, numerous fine pores (20–40 A radius) form perpendicular to the crystal surface from which the gases vent. This is accompanied by an increase in the surface area from about 120 to about 230 m2/g (N2/BET) and a doubling of the pore volume (0.6 to 1.0 cm3/g, Hg intrusion). The bulk aluminum changes from all octahedral to about 20% tetrahedral-80% octahedral. Auger spectroscopy did not appear to indicate changes in the surface aluminum environment. The X-ray powder pattern changes from that of a diffuse hydrotalcite to a very poor magnesium oxide pattern.

Pulse microreactor examination of the vapor-phase aldol condensation of acetone

Abstract Pulse microreactor techniques and a small flow reactor have been employed to examine the nature of the MgOAl 2 O 3 -catalyzed aldol condensation of acetone to principally mesityl oxide and isophorone. It has been shown that a large number of transient intermediates are involved in a series of very rapid, reversible equilibria. The last step in this sequence is the irreversible formation of isophorone which appears to be the net driving force of this condensation reaction. The nature of the catalyst, the effect of various additives, and the reaction intermediates and by-products have been detailed in order to arrive at an overall description of the base-catalyzed oligomerization of acetone.

Role of silanol groups in formation of supported chromocene catalysts

Abstract Deposition studies have established maximum values for the adsorption of chromocene on dehydroxylated silicas. The process of chemisorption of chromocene changes from reaction of predominantly two to one hydroxyl group as the temperature of silica increases from 100 to 800 °C. Chromocene, deposited on Cab-O-Sil type silicas heated at 200 and 400 °C, formed highly active catalysts for ethylene polymerization. Results from studies with this support are compatible with an active site model which involves reaction of chromocene with free, isolated silanol groups. Sterically hindered hydroxylic compounds such as triphenylsilanol and t-butanol react in solution with chromocene to form dimeric cyclopentadienyl chromium alkoxides. These chromium compounds do not show catalytic activity for ethylene polymerization under conditions typical for the ( C 5 H 5 ) 2 Cr SiO 2 catalyst. Furthermore, deposition of these new chromium compounds on silica did not provide, in most cases, a route to catalytic activity. However, the addition of alkylsilanes to these supported chromium compounds did lead to active catalysts. The polymerization behavior of these catalysts resembles the supported chromocene catalyst. These overall results lend support to an active site model previously described.

The nature of the hydrolysis of chlorobenzene over calcium phosphate apatite

In the second stage of the Raschig phenol process chlorobenzene is hydrolyzed at 375–450 ° to phenol over what has now been found to be a calcium hydroxyapatite catalyst: 2C6H5Cl + Ca10(OH)2(PO4)6 → 2C6H5OH + Ca10Cl2(PO4)6. Steam, admitted simultaneously with the chlorobenzene, regenerates the hydroxyapatite: 2H2O + Ca10Cl2(PO4)6 → 2HCl + Ca10(OH)2(PO4)6. The best catalytic performance is obtained from a high surface area (50–100 m2/g), partially amorphous calcium phosphate apatite prepared by an aqueous precipitation procedure. The calcium ions can be isomorphously replaced with strontium, barium and the phosphate ions by arsenate ion, etc., to also yield active catalysts. Similar apatites prepared by high temperature techniques and the other calcium phosphates are not catalytically active. Copper (II) is a highly effective cocatalyst, while other transition metal ions are inactive. The mechanism of the chlorobenzene hydrolysis reaction seems to be a nucleophilic displacement of the aryl-chloride by hydroxide with substantially complete retention of substituent position on the benzene ring. Any benzyne component of this reaction is less than 5%.

The nature of the decomposition of phenylvanadium oxide dichloride

The reaction of diphenylmercury and vanadium oxide trichloride in cyclohexane solution at 25° initially yielded phenylmercuric chloride and the unstable phenylvanadium oxide dichloride whose decomposition has been studied. When a diphenylmercury/vanadium oxide trichloride ratio > 1 was employed, the biphenyl formation rate was accelerated and more than one chlorine on the vanadium was replaced by a phenyl group. When this ratio was < 1, the rate of biphenyl appearance was retarded and, on acid hydrolysis, benzene, phenol and biphenyl were recovered. It was shown that all cyclohexane-soluble, phenyl-bearing species (e.g. PhnVOCl3-n, Ph2Hg) interchanged phenyl groups very rapidly. The appearance of biphenyl was thought to be due to the concerted decomposition of an unstable di-σ-phenylvanadium intermediate.

The pyrolysis of phenyltin benzoates and related substances

Abstract When diphenyltin dibenzoate is subjected to pyrolysis at 300°, almost exactly two moles of benzene (plus a small amount of biphenyl) are recovered and a non-volatile residue is left behind: (C 6 H 5 ) 2 Sn(O 2 CC 6 H 5 ) 2 → 2 C 6 H 6 + Sn(O 2 CC 6 H 4 ) 2 Chemical degradation of this residue shows that the benzene originated from the tin-bound phenyl groups, that the hydrogen is abstracted from the benzoic acid residue, and that new SnC bonds had formed between the metal and the benzoate group. There is no significant reduction of Sn IV . When this pyrolysis is carried out in cumene, no interaction products of phenyl radicals and cumene are observed. It appears that this reaction is probably not of the classical homolytic type. Triphenyltin benzoate, on pyrolysis at 350°, loses two phenyl groups almost exclusively as benzene. Diphenylantimony benzoate loses two phenyl groups as benzene (400°) and phenylmercury benzoate loses one phenyl group (as benzene), as well as a molecule of carbon dioxide (300°), leaving a residue of (C 6 H 4 Hg) n . Neither diphenylarsenic benzoate nor triphenylsilyl benzoate decompose at 400°.

Three coordinated complexes of copper(I).

Copper, the last transition metal in the first row of the periodic table, is in many ways unique. For reasons that are not always clear, its range of catalytic effectiveness in chemical reactions is almost unrivaled. Copper compounds are catalytically highly effective in numerous biochemical processes, organic and inorganic redox reactions, nucleophilic aromatic displacements, photochemical reactions, peroxide and azo decompositions, halogenations, and hydrogenations. Stable olefin, actylene, and aromatic a-complexes are also formed by Cu(1) compounds. Many of these reactions are catalyzed by or involve Cu(1) complexes. Cu(1) is a d1O ion and is isoelectronic with Ni(0) (or Zn (11)) :