Ethyl methyl ketone, protonated

Examination of two acidic hydrogens in 2-pentanone (36) shows that the pKa of Ha is about 20 and that of is about 21. Proton H, (in violet) 36 is attached to an a-carbon that also has an ethyl group attached to it. The a-carbon that bears Hg (in red) has only hydrogen atom attached to it. As noted earlier, an alkyl group is electron releasing relative to the a-carbon of a ketone or aldehyde, so Hb is less polarized than H (it has a smaller 6-1-). This observation is consistent with the observation that Hb is less acidic. 2-Pentanone (32) is called an unsymmetrical ketone because two different groups are attached to the carbonyl (the common name of 32 is ethyl methyl ketone, which reflects the fact that it is unsymmetrical). In an unsymmetrical ketone with different substituents on the different a-carbons, it is possible that those two a-protons will have different pKg values and that one may be more acidic than the other. 

Variations of the malonic ester and acetoacetic ester sequenees lead to many useful synthetic opportunities. In the examples quoted, the base-solvent pair used was ethanol-sodium ethoxide, where the alkoxide is the conjugate base of tbe solvent. If NaOEt-EtOH were used with a methyl ester, transesterification would give a mixture of methyl and ethyl esters as products. For both malonic ester and acetoacetic ester removal of the most acidic proton (a to both carbonyls) also gives the more thermodynamically stable enolate. Either NaOEt-EtOH or LDA-THF will generate the desired enolate. The malonic ester synthesis is most useful for the synthesis of highly substituted monoacids, and tbe acetoacetic ester synthesis is used to prepare substituted methyl ketones. 

An analogous approach is the stabilization of phosphonium ions by addition of phos-phanes (PMcs, PEts, PPhMca, and PPhaMe) to methyl ketones (acetone, methyl ethyl ketone, 1,1,1-trifluoroacetone, and fluoroacetone) in an aqueous solution of Ga4L (Scheme 10.4). These cations decompose in water but they are persistent for weeks in the nanovessel. However, this stability is pH-dependant. The pH should be low because the guest should be protonated and is regularly exposed to the bulk of water as a consequence of the dynamic behavior of the assembly, but the pH should not be too low because in that case the host would disassemble. Therefore, the optimal value is 5.2. The exact mechanism is still unknown it has been ascertained that the protonated phosphane can be encapsulated but it is not possible to determine where the addition to the ketone occurs, inside or outside the cavity. Due to the chirality of the Ga4L tetrahedron, a kinetic diastereoselectivity is also obtained with chiral ions leading to diastereomeric excesses of 30-50%. 

The base, however, acts to abstract the proton from the a-haloketones to produce the a-halocarbanion. The latter is immediately removed by the reaction with the free, uncomplexed organoborane, and the transfer of alkyl group from boron occurs and product methyl ketone is obtained by the hydrolysis of the intermediate (Scheme 7.4) [2c]. It is significant to mention that protonolysis of the reaction intermediate by 2,6-di-f-butylphenol produced in the reaction is relatively difficult. Consequently, ethyl alcohol is added to liberate ketone. 

The asymmetric catalysis using SiCU and (107) is effective also in enantioselective Mukaiyama aldol reaction of TMS enolates derived from methyl ketones [164]. Addition of i-Pr2NEt improves the yield of adducts. The amine probably acts as a proton scavenger to suppress the protodesilylation of the enolates with adventitious HCl. The reaction of TMS enolates derived from ethyl ketones shows high anti diastereoselectivity as in the case of the TBS enolate of t-butyl propanoate. 

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

The molecular ion can be very small or nonexistent. Esters where R is greater than methyl form a protonated acid that aids in the interpretation (e.g., m/z 47, formates m/z 61, acetates m/z 75. propionates m/z 89, butyrates etc.). Interpreting the mass spectra of ethyl esters may be confusing without accurate mass measurement because the loss of C2H4 can be confused with the loss of CO from a cyclic ketone. 

Enantioselective hydrogenation of prochiral ketones has rarely been studied in aqueous biphasic media. In addition to the chiral bisphosphonic acid derivatives of 1,2-cyclohexanediamine [130], the protonated 4,4 -, 5,5 -, and 6,6 -amino-methyl-substituted BINAP (diamBINAP 2HBr) ligands (Scheme 38.7) served as constituents of the Ru(II)-based catalysts in the biphasic hydrogenations of ethyl acetoacetate [131, 132]. These catalysts were recovered in the aqueous phase and used in at least four cycles, with only a marginal loss of activity and enantio-selectivity. 

The first report of the preparation of the dialkyl succinimide (29-3) dates back to early in the twentieth cenmry. It is consequently surprising to note that it was introduced as an anticonvulsant, under the name ethosuximide, well after its more recently synthesized congeners. The synthetic route starting from methyl ethyl ketone generally follows that above with the exception of the use of ammonia in the last step. The compound thus differs as well by possessing a somewhat acidic imide proton [30]. 

Other hemiacetals which have been prepared include the methyl 8<9a>, ethyl 9b), and isopropyl hemiacetals 81) of tetramethylcyclopropanone, the phenyl, a- and (3-naphthyl hemiacetals of cyclopropanone 82>, and the benzyl hemiacetal of 2,3-di-f-butylcyclopropanone. 13> In the last case, the benzylic methylene protons display an AB pattern in the PMR spectrum indicating that the two Ybutyl groups are trans to one another. Although derivatization of this di-f-butyl ketone was possible, carbonyl addition may be hindered by steric factors as suggested by the lack of reaction of 2,2-diY-butylcyclopropanone with methanol. 55a>... 

Diacidic phosphonates (Vla-VId), i.e., those with two protons available for substitution, had a tendency to yield significant a-mounts of bis-substituted phosphonates [(RiC0CH20)2P0(R2) ] upon reaction with IV. However, it was found that careful addition (Table I) of the a-diazoketone to the phosphonate at reaction temperature minimized the formation of this by-product moreover, the bis-substituted phosphonates could be converted to the corresponding monoacids by refluxing the former with sodium iodide in methyl ethyl ketone. In this manner higher yields of phosphonates (e.g., Vllla-VIIId) could be obtained. 

The compositionMeCo(PR3)4 isreahzed, apart from PMes, with various phosphines. The PPhs complex, however, has a lower coordination number, that is, MeCo(PPh3)3 is found in the solid, but it partially dissociates in solution into MeCo(PPh3)2, reminiscent of the behavior of RhCl(PPh3)3 (see Wilkinson s Catalyst). In protic solvents, this compound decomposes by proton abstraction, releasing methane, and this observation may explain its abihty to effect aldol condensation of certain ketones (acetone and methyl ethyl ketone) in an aprotic solvent (equation 36). 

Unsubstituted malonate esters and ethyl acetonate give highest yields, while methyl substituted analogs are less effective. Esters and ketones enolates are do not undergo allylic alkylation, and instead induce proton abstraction, generating acyldienes. There seems to be competition between nucleophilic attack and proton abstraction when utilizing unstable carbanions. ... 

Gtmnal alkylation af ketones. Coates and Sowerby have reported a new method for site-selective geminal alkylation of ketones which involves reduction of the n-butylthiomethylene derivative of the ketone by lithium-ammonia to give a methyl-substituted cnolatc anion which can be alkylated in situ. The ketone, for example cyclohexanone (I), is condensed with ethyl formate and then transformed into the n-butylthiomethylene derivative (2) by reaction with n-butyl mercaptan (2, 53-54). This is then reduced with excess lithium in liquid ammonia at -33° with 2 eq. of a proton donor (water is usually used to avoid ovcralkylation). The lithium cnolate is then... 

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