Decomposition of aluminum alkyls

The decomposition of aluminum alkyls, such as (CH3)3A1 or ( 2115)3Al, in an oxidizing atmosphere, such as O2 orN20, produces alumina deposits in a temperature range of 250-500°C.l l... 

In addition to these lowtemperature thermal processes, aluminum can be deposited by the decomposition of an alkyl precursor with a UV laser, or with an argon-ion laser in applications such as patterns and... 

Subsequent addition to the solid phase of an amount of inactive alkyl-aluminum in solution and decomposition of all alkyl-metal bonds with 10 % H2SO4. 

A great advantage of the borates is that the ratio of borate to metallocene is about 1 to 1 and not 5000 to 1, as in the case of MAO for homogeneous systems. On the other hand, the borate system is highly sensitive to poisons and decomposition and must be stabilized by addition of aluminum alkyls such as triisobutylaluminum (TIBA) the necessary ratio of TIBA to zirconocene is in the range of 100-500. 

It is noteworthy that the transition metals that serve as hydroaluminating catalysts are also active in establishing the equilibrium between aluminum alkyls and their decomposition products, aluminum, hydrogen and alkene (equation 12). Accordingly, these metals, in addition to hafnium, niobium, vanadium, scandium and lanthanum, have found use as activators for the direct synthesis of aluminum alkyls (equation 12, to the left). Probably most of these metal salts will also be capable of accelerating the hydroalumination reaction. 

Thermal stability of aluminum alkyls is highly dependent upon the ligands bonded to aluminum. For example, triethylaluminum is stable up to about 120 °C (37) and its initial mode of decomposition is by )S-hydride elimination to generate diethyl-aluminum hydride and ethylene (eq 4.20). Diethylaluminum hydride may decompose further to aluminum, hydrogen and two additional equivalents of ethylene (eq 4.21). The overall equation for decomposition is shown in eq 4.22. 

Reduction of l-methyl-2-alkyl-.d -pyrroline and l-methyl-2-alkyl-.d -piperideine perchlorates with complex hydrides prepared in situ by partial decomposition of lithium aluminum hydride with the optically active alcohols (—)-menthol and (—)-borneol affords partially optically active l-methyl-2-alkyl pyrrolidines (153, n = 1) and 1-methy 1-2-alkyl piperideines (153, n = 2), respectively (241,242). 

Pierson, H. O., Aluminum Coatings by the Decomposition of Alkyls, Thin Solid Films, 45 257-264 (1977)... 

Deposition by the hydrogen reducti on of the trihalides (A1X3) i s not practical because of the stability ofthe latter, but is possible through the disproportionation ofthe monohalides. This is a difficultprocedure which has been largely supersededby the decomposition of the aluminum alkyls mentioned above. ... 

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

As shown in Table XIV, the reactivity of (trichloromethyl)silanes varied depending upon the substituent on silicon. The reactivity and yields of (trichloromethyl)-methyldichlorosilanes were slightly higher than those of (trichloroinethyl)tri-chlorosilanes in the aluminum chloride-catalyzed alkylation as similarly observed in the alkylations with (ai-chloroalkyl)silanes and (dichloroalkyl)silanes. The electron-donating methyl group on the silicon facilitates the alkylation more than the electron-withdrawing chlorine. The minor products, (diphenylmethyl)chloro-silanes, were presumably derived from the decomposition of (triphenylmethyl)-chlorosilanes. 

As in sulfuric acid alkylation, the hydrocarbon-acid emulsion passes from the contactor into an acid settler for separation of acid and hydrocarbon phases and the acid layer recirculates to the reactor. Unlike sulfuric acid, however, hydrofluoric acid is appreciably soluble in hydrocarbons, and as much as 1% by weight may be retained in the hydrocarbon layer. The necessity of recovering this acid from the hydrocarbon phase results, in another difference between hydrofluoric and sulfuric acid processing in that a hydrofluoric acid stripper is required. This stripper is ordinarily packed with aluminum rings which serve not only as tower packing but also as a catalyst for the decomposition of organic fluorides into hydrocarbons and free hydrofluoric acid. 

A RAIR spectrum of the n-butyl surface species on Al(100) has been reported at 335 K in the fCH3/pCH2 region (203). A fCH3/pCH2 RAIR spectrum has been reported for the isobutyl group formed by the decomposition of triisobutylaluminum on Al(100) at 335 K (203), and a VEEL spectrum has been obtained from decomposition of the trialkyl-aluminum on Al(lll) at 100 K (204). These alkyl surface species are stable to 450-500 K and then decompose to give the expected alkenes by /3-H elimination. 

Several authors have studied the reaction products in the Lewis acid catalyzed decomposition of phenyl and alkyl azides.179-185 Hoegerlee and Butler have found that phenyl azide forms a hydrocarbon-soluble complex at —70° with triethylaluminum, diethylchloroaluminum, and ethyldichloro-aluminum. 1 Upon warming to room temperature, this complex slowly decomposes into an intermediate phenylimine-aluminum compound (25) which then rearranges into a variety of amidoalkylaluminum reaction products (RP) (eq 4). 

Kreher and Jager have studied the aluminum chloride catalyzed decomposition of azidoformates in several solvents.18118 They reasonably assumed that the decomposition process in n-hexane and nitromethane solution proceeds by C02 elimination and the formation of alkyl azides which then decompose into imines (eq 5). Furthermore, infrared analysis has shown that the catalyst is fixed at the carbonyl group of the azido-formate. 

This reaction may involve stepwise addition of the two equivalents of PhNCS via a 3-membered ring intermediate, RN—S—C=NPh.66 A thia-ziridine was also suggested by Borsche67 to explain the formation of 4-phenyl-5-phenylimino-l,2,4-dithiazolidine-3-thione from the aluminum chloride-catalyzed decomposition of phenyl azide in carbon disulfide. If a 4-substituted thiatriazoline is formed from phenyl isothiocyanate and the alkyl azide, the reaction may then be formulated as indicated in Eq. (21). This scheme is supported by the recent findings of Neidlein and... 

Methyl />-tolyl sulfone has been prepared by oxidation of methyl 7>-tolyl sulfide with hydrogen peroxide 4 r or ruthenium tetroxide,6 by alkylation of sodium -toluenesullinate with methyl iodide 7,8 or with methyl potassium sulfate,9 by decarboxylation of -tolylsulfonylacetic acid,7 by thermal decomposition of tetramethylammonium -toluenesulfinate,10 by reaction of cw-bis-(%tolylsulfonvl)-ethene with sodium hydroxide (low yield),11 by the reaction of methanesulfonyl chloride with toluene in the presence of aluminum chloride (mixture of isomers),12 by... 

Ph(PhOMe)2C][B(C6F5)4] and [(PhOMe)3C][B(C6F5)4] are more stable compounds and do not react with aluminum alkyls. Lower reactivity against aluminum alkyls results in an increase in the apparent catalytic activity (Figure 17.7). The decomposition of the borate by TIBA is observed by H NMR and the excess amount of borate increases the catalyst activity. 

As described in Section III.B.l, decomposition of primary alkoxides in inert organic solvents requires temperatures much higher than 300°C, but in alcohols they may decompose at relatively low temperatures. The carbocation formed by the heterolytic cleavage of the C-0 bond is only poorly solvated in the inert organic solvent therefore the reaction barely proceeds. On the other hand, in alcohols, carbocation is solvated, which lowers the activation energy for the decomposition of alkoxide. For example, aluminum ethoxide does not decompose in toluene at 300°C, while it does decompose in ethanol, yielding the alkyl derivative of boehmite. 

If, however, one of the ethyl groups in triethylaluminum is replaced by an ethoxide ligand, the resultant molecule is dramatically more stable thermally. For example, diethylaluminum ethoxide is stable up to at least 192 °C (37). A comparison of the percent decomposition of selected aluminum alkyls over 3 hours at °C is shown... 

H1 nuclear magnetic resonance measurements have established that, at least for the dialkyl alkynyl alanes, bridge bonds are formed exclusively by the a-carbon atom of the alkynyl group (30). This bond is stronger for the alkynyl than for the alkenyl compounds. In accordance with this, the dialkylalkynyl alanes may be distilled at reduced pressure as dimers without decomposition, whereas the corresponding alkenyl compounds decompose when heated and then undergo further reaction, in which addition of the A1—C bond to the C=C double bond occurs. The resulting aluminum alkyls disproportionate subsequently to trialkylalane and polymeric compounds (253). 

On decomposition of the 1 1 adduct of phenyl azide with both alkyl aluminum chlorides, the main reaction is A-ethylation with the formation of IV-ethylanilides 100). 

The addition of metal and metalloid hydrides to carbon-carbon double bonds is not a new reaction, having been observed from time to time with silanes of the type R3SiH under free-radical conditions (4%, 85) and with boron hydrides (68). The versatility of such hydride-olefin interactions, nevertheless, first became evident with the recent researches of Ziegler with lithium and aluminum alkyls (139). The observation that attempted distillation of ethyllithium led to decomposition into lithium hydride, ethylene, and higher olefins prompted the following formulation of the reaction course (see 18) ... 

With increasing temperature the As-B adducts convert to the N-B adduct, except for the (-Pr compound, which is stable at room temperature, and decomposition leads to the formation of Me2AsAsMe2, Me2AsH, [R2NBH2]2, and R2NH-BHs. The results from the aluminum alkyl reactions have been used to develop new syntheses to tertiary arsines (see Section 2). 

Microporous solids with surface areas in the range of 400 m /g or larger can be prepared in several ways. Controlled thermal decomposition of silica gel or aluminum hydroxides to AIO(OH) and then to the 7- or r/-phases of alumina produces such high-surface-area materials. The so-called sol-gel method, which uses both aluminate and silicate ions or aluminum and silicon alkyl compounds at a well-controlled hydrogen ion concentration, produces crystalline microporous solids that... 

Besides the /3-H elimination mechanism, chain transfers to aluminum and to the monomer can occur. Also, /3-alkyl abstraction has to be considered. The homolytic cleavage of the transition metal—carbon a-bond should only play a minor role (decomposition of the catalyst). 

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