Acetone acid-base properties

Zaki, M.L, Hasan, M.A., and Pasupulety, L., Surface reactions of acetone on AljO, TiOj, ZrO-, and CeOji IR spectroscopic assessment of impacts of the surface acid-base properties, Langmuir, 17, 768, 2001. 

Ivanov et al. studied the MPV reaction between ethanol and acetone over various metal oxides having different acid-base properties [13]. Reaction was found to occur over both Lewis acid (AI2O3-CI) and base (MgO, Zr02) catalysts. Based on FT-IR and specific poisoning experiments, two mechanistic variants were proposed differing in the mode of formation of... 

The reactions of 3-methylbutynol were first recommended by Lauron-Pernot et al. to characterize the acid-base properties of a series of metal oxides. The basic centres catalyze the cleavage reaction of MBOH, which produces acetone and acetylene, while the acid centres catalyze the dehydration of MBOH to 3-methyl-3-buten-1-yne (MBYNE) or the intermolecular rearrangement to produce 3-methyl-2-butenal (PRENAL). The production of 3-methyl-3-butene-2-one (MIPK) and 3-hydroxy-3-methyl-... 

Mg-Al mixed oxides obtained by thermal decomposition of anionic clays of hydrotalcite structure, present acidic or basic surface properties depending on their chemical composition [1]. These materials contain the metal components in close interaction thereby promoting bifunctional reactions that are catalyzed by Bronsted base-Lewis acid pairs. Among others, hydrotalcite-derived mixed oxides promote aldol condensations [2], alkylations [3] and alcohol eliminations reactions [1]. In particular, we have reported that Mg-Al mixed oxides efficiently catalyze the gas-phase self-condensation of acetone to a,P-unsaturated ketones such as mesityl oxides and isophorone [4]. Unfortunately, in coupling reactions like aldol condensations, basic catalysts are often deactivated either by the presence of byproducts such as water in the gas phase or by coke build up through secondary side reactions. Deactivation has traditionally limited the potential of solid basic catalysts to replace environmentally problematic and corrosive liquid bases. However, few works in the literature deal with the deactivation of solid bases under reaction conditions. Studies relating the concerted and sequential pathways required in the deactivation mechanism with the acid-base properties of the catalyst surface are specially lacking. 

The activity and selectivity for acetone oligomerization on MgyAlO oxides depend on the catalyst acid-base properties, which in turn are determined by the aluminum content in the sample. Mg-rich catalysts selectively yield mesityl oxides whereas Al-rich Mg AlOx oxides produce mainly isophorone. Mg AlO samples are more active than alumina. Intermediate Mg/Al compositions show unique catalytic properties because fiilfil the reaction requirements for the... 

The MgyAlOx activity declines in the acetone oligomerization reaction due to a blockage of both basic and acid active sites by a carbonaceous residue formed by secondary aldol condensation reactions. The key intermediate species for coke formation are highly unsaturated linear trimers that are formed by aldol condensation of mesityl oxide with acetone and remain strongly bound to the catalyst surface. The catalyst surface acid-base properties determine the preferential formation of a given trimeric intermediate, which in turn defines the chemical nature of the carbon deposit. Aromatic hydrocarbons are the main component of coke formed on acidic Al-rich MgyAlOx samples whereas heavy a,P-unsaturated ketones preferentially form on basic Mg-rich catalysts. 

Catalytic Reactions. Catalytic reactions often give a very good measure of the basic properties of the solid surfaces. The reaction of 2-methyl-3-butyn-2-ol (MBOH) has been used to judge the acid-base properties of the solid surfaces (5). Acetone and acetylene are obtained over solid bases such as MgO, while 3-methyl-3-buten-l-yne is obtained over solid acids such as P205/Si02. Furthermore, amphoteric oxides such as Zr02 give 3-hydroxy-3-methyl-2-butanone. 

Base-catalyzed reactions were reviewed in general by Hattori [208,222], and from the reactions described butene isomerization, alcohol conversion, toluene alkylation, acetone condensation/diacetone alcohol decomposition, Knoevenagel condensations, diketone cyclization, ring transformation reactions, and dimerization of aldehydes to the corresponding esters were used to evaluate the acid-base properties in molecular sieves. 

The organic solvents most commonly used in the extraction-preconcentration step and sample dilution are hexane, methanol, ethyl ether, ethyl acetate and acetone. When determination involves the separation of compounds with different acid-base properties, i.e. acidic, basic and neutral analytes, separation occurs as a function of pH acidic and basic molecules are extracted making use of hydro-organic mixture also containing acids or bases while neutral species are dissolved in organic phases. 

The acid-base properties have been estimated using IPA decomposition in the temperatures range 200-350°C (table 1). In all case, propylene and acetone were detected. For the monophasic HT-sample, the IPA is mainly dehydrogenated into acetone and, in less extend, dehydrated to propylene. In contrast, for all polyphasic CP-samples, IPA is predominantly dehydrated into propylene (up to 99% of selectivity). The selectivity towards dehydrogenation and dehydration reactions was much affected by changing the reaction temperatuie and preparation method. The temperatuie of calcination did not influence markedly the products distribution. 

Both acid and base sites are required for the cascade. ZnO and Zr02 act as a weak base and an acid respectively. Both oxides per se are not active and selective for the aldol condensation step of acetone to mesityl oxide, while a 2 8 physical mixture of ZnO and Zr02 promotes the aldol condensation by changing the acid-base properties of the oxides at the grain boundaries. 

Both uncalcined and calcined LDHs have also been shown to be effective supports for noble metal catalysts [18-25]. For example, palladium supported on Cu/Mg/Al LDHs has been used in the liquid phase oxidation of limonene [24], and on calcined Mg/Al LDHs for the one-pot synthesis of 4-methyl-2-pentanone (methyl isobutyl ketone) from acetone and hydrogen at atmospheric pressure [25]. In the latter case, the performance depends on the interplay between the acid-base and hydrogenation properties. More recently. 

Lewis base properties a. Aptotic b. Hydrogen bond donor 7. Negligible Lewis acid or <25 + Pyridine, acetone, tetramethylurea, acetic anhydride Ethylenediamine... 

Among the cosolvents studied, methanol and acetone have received the greatest interest (36-38). Methanol may act as either a Lewis acid or a Lewis base while acetone is a weaker Lewis base and very slightly acidic ( ). The dipole moment of acetone is 2.88 Debeye compared to 1.7 Debeye for methanol. Based on these properties, Walsh, et al., (40), interpret the data of Van Alsten (37) and Schmitt (38) and present liquid phase IR measurements which show Lewis acid-base interactions in the systems methanol/acridine and acetone/benzoic acid. Supercritical solubility data of Dobbs, et al., ( ), exhibit trends which indicate the importance of acid-base interactions. Van Alsten and Schmitt present data which show that acid-base interactions are a secondary cosolvent effect superimposed on a primary effect determined by cosolvent concentration. 

The reaction is further complicated by thermodynamic equilibrium limitations, as indicated in Table I. The condensation/dehydration of acetone to MO is limited to about 20% conversion at 120 C (16). However, there is no equilibrium limitation to the overall acetone-to-MIBK reaction. This, coupled with the possibility of numerous thermodynamically favorable side reactions that are also acid/base-catalyzed (Fig. 1), suggests the need to balance the acid/base and hydrogenation properties of the selected catalyst. 

Properties Wh. fine cryst. powd., odorless very sol. in dimethyl sulfoxide, dimethyl formamide sol. in acetone (reacts), strong acids, bases mod. sol. in ethanol, polyalkylene glycols insol. in benzene, ethylene dichloride, gasoline, cold water sp.gr. 1.53 decomp. pt. 158-160 C gas yield 125 cc/g STP gas 91% Nj, 9% H O... 

Properties Bm. powd. sol. 10-50 mg/ml in DMSO sol. 1-5 mg/ml in water, 95% ethanol sol. < 1 mg/ml in acetone m.w. 234.20 m.p. 285 C (dec.) Toxicology LD50 (oral, rat) 6920 mg/kg local irritant severe eye irritant may irritate skin, mucous membranes TSCA listed Precaution Probably combustible may react with strong oxidizing agents, min. acids, bases may be sensitive to prolonged exposure to air... 

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