Acetone scavenger

The most commonly used protected derivatives of aldehydes and ketones are 1,3-dioxolanes and 1,3-oxathiolanes. They are obtained from the carbonyl compounds and 1,2-ethanediol or 2-mercaptoethanol, respectively, in aprotic solvents and in the presence of catalysts, e.g. BF, (L.F. Fieser, 1954 G.E. Wilson, Jr., 1968), and water scavengers, e.g. orthoesters (P. Doyle. 1965). Acid-catalyzed exchange dioxolanation with dioxolanes of low boiling ketones, e.g. acetone, which are distilled during the reaction, can also be applied (H. J. Dauben, Jr., 1954). Selective monoketalization of diketones is often used with good success (C. Mercier, 1973). Even from diketones with two keto groups of very similar reactivity monoketals may be obtained by repeated acid-catalyzed equilibration (W.S. Johnson, 1962 A.G. Hortmann, 1969). Most aldehydes are easily converted into acetals. The ketalization of ketones is more difficult for sterical reasons and often requires long reaction times at elevated temperatures. a, -Unsaturated ketones react more slowly than saturated ketones. 2-Mercaptoethanol is more reactive than 1,2-ethanediol (J. Romo, 1951 C. Djerassi, 1952 G.E. Wilson, Jr., 1968). 

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Furanic black resins arising from furfural, furfuryl alcohol and furfurylidene acetone 3a are characterized by highly conjugated structures (6-8) their inhibiting power as radical scavengers was tested and turned out to be extremely nigh even in heterogeneous conditions, e.g. with the resin suspended in a monomer solution. 

Acetylene is widely sold as the fuel for welding torches, and it is stored in large cylinders at high pressures in many welding shops. In fact, this acetylene is mixed with acetone, which has been found to be an effective scavenger of acetylene decomposition, so that these tanks are relatively safe. 

This test does not require expensive equipment and permits screening of many compounds in a single day. It has been used for drugs such as fiuoroquinolones as shown in Figure 19.3 [20-22], and even for insoluble pigments such as titanium dioxide [23, 24]. Poorly water-soluble chemicals can be tested as dispersions in organic solvents added to the buffer. However, solvents that may scavenge ROS (e.g., DM SO, ethanol) should be avoided, whereas acetone or acetonitrile are preferable. 

In cases where metals or metal ions can contaminate the products, reaction vessels fabricated from inert polymeric materials restrict that possibility. A significant example involved the reaction of maltol with aqueous methylamine to give l,2-dimethyl-3-hydroxypyrid-4-one. The product is a metal chelator employed for the oral treatment of iron overload. Consequently, it is an excellent metal scavenger but must be produced under stringent conditions that preclude metal complexation. Literature conditions involved heating maltol in aqueous methylamine at reflux for 6 h, the product was obtained in 50% yield, but required decolourisation with charcoal135. With the CMR, the optimal reaction time was 1.3 min, and the effluent was immediately diluted with acetone and the near colourless product crystallised from this solvent in 65% yield (Scheme 9.18). A microwave-based batch-wise preparation of 3-hydroxy-2-methylpyrid-4-one from maltol and aqueous ammonia was also developed. 

Evidence for the formation of H3Oaq as intermediate may be derived from competition kinetics. When the scavenging reactivity of H30 + toward eaq was compared with acetone by competition (79), it was found half as effective as expected from the specific rate constants obtained directly. This may suggest the reaction H30 + (CH3)2CO - H30 + + (CH3)2CO-. In another study, the competition for e aq between H30 + and N20 showed the latter to be more effective as expected from the known rate data (4, 111), suggesting again H30 + N20 - H30 + + N20 -. 

The residual yield using phosphate ion as the scavenger, but has a small positive value using N20, or acetone. We attribute this to a salt effect promoting recombination ... 

One of the most used resins in solid-phase combinatorial organic synthesis, which has found a myriad of applications, is the Merrifield resin (17).61 This resin is also the building block for a tremendous amount of novel resins being developed in combinatorial chemistry with applications in both solid-phase as well as solid-phase-assisted solution-phase combinatorial chemistry. A recent, useful, and novel example is the report of its being employed as a triphenylphosphine scavenging resin.76 During the conversion of azidomethylbenzene (51) into benzylamine, excess triphenyl-phosphine is allowed to react with Merrifield resin (17) in the presence of sodium iodide in acetone. A phosphonium-substituted resin (52) is thus formed. Upon simple filtration, pure benzylamine is isolated as shown in Fig. 22. 

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