5.5- Dimethyl-1,3-cyclohexanedione, reaction with

Acetaldehyde can be isolated and identified by the characteristic melting points of the crystalline compounds formed with hydrazines, semicarbazides, etc these derivatives of aldehydes can be separated by paper and column chromatography (104,113). Acetaldehyde has been separated quantitatively from other carbonyl compounds on an ion-exchange resin in the bisulfite form the aldehyde is then eluted from the column with a solution of sodium chloride (114). In larger quantities, acetaldehyde may be isolated by passing the vapor into ether, then saturating with dry ammonia acetaldehyde—ammonia crystallizes from the solution. Reactions with bisulfite, hydrazines, oximes, semicarb azides, and 5,5-dimethyl-1,3-cyclohexanedione [126-81 -8] (dimedone) have also been used to isolate acetaldehyde from various solutions. 

The assay for formaldehyde is today mainly performed by either of two general methods. The one most widely used depends on the reaction of 5,5-dimethyl-1,3-cyclohexanedione (Dimedon) with formaldehyde when applied after the destruction of excess periodate, it proceeds quantitatively,... 

Cycloaddition Reactions with Other Nucleophiles The anodic two-electron oxidation of catechol affords o-quinone that may react with the enolates of 4-hydroxycoumarine or 5,5-dimethyl-1,3-cyclohexanedione (dimedone). The resulting adducts undergo a second anodic oxidation leading to benzofuran derivatives in good yields (90-95%) (Scheme 53) [75, 76]. 

The reaction of 2,2-disubstituted 1,3-cyclohexanediones 1 with dimethyl methanephosphonate in THF in the presence of LDA gives 3-substituted 2-cyclohexenones 2 in moderate to very good yields. 

On the other hand y-pyrones or 1,3-diketones could be obtained from the reactions of ketone derived enamines with diketene 423-426). The addition of dimethyl ketene dimer to aldehyde or ketone derived enamines produced cyclohexanediones 425,426). 

Ethyl-/3-methylglutaric acid has been prepared by the acid hydrolysis of a,a -dicyano- S-ethyl-fl-methylglutarimide, 3-cy-ano-4-ethyl-6-imino-2-keto-4-methylpiperidine-5-carboxamide or the diimide of 8-ethyl- 9-methylpropane-a,a,a, a -tetracarboxylic acid by the oxidation of jS-ethyl-fl-methyl-5-valerolactone with chromic acid and by the reaction of sodium hypobromite on l,4-dimethyl-l-ethyl-3,S-cyclohexanedione. ... 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

Reaction of 5,5-dimethyl-l,3-cyclohexanedione and arylidenemalononitrile gave 5, and of 1,3-diarylthiobarbituric acids with hippuric acid and triethyl orthoacetate or triethyl orthoformate and malononitrile or alkylnitriles gave pyranopyrimidines 6 or 7. Pyranopyrimidines 8 were obtained from reaction of arylidenemalononitriles or N-phenyl maleimides with barbituric acid . ... 

Selenium has been determined with 5,5-dimethyl-1,3-cyclohexanedione [51], 6-amino-1-hydroxynaphthalenesulphonic acid [52,53], and l-aminonaphthalene-7-sulphonic acid [54], Determinations of Se involved also the following dyes Rhodamine B [55], Methylene Blue [56], Xylenol Orange [57], and Rhodamine 6G (by the amplification method, in iodide medium, after oxidation of iodide to iodine, and reaction of the I03 with the dye) [58]. 

Treatment of 5,5-dimethyl-l,3-cyclohexanedione with NaOCl and KOH in aqueous solution at 35°C, followed by acidification of the reaction mixture, leads to the formation of 3,3-dimethylpentanedioic acid. Propose a detailed mechanism to account for the formation of this product. 

A dried 10 mL round-bottomed flask was charged with aromatic aldehyde (1 1.0 mmol), cyclic 1,3-diketone (2 1,3-cyclohexanedione or 5,5-dimethyl-l,3-cyclohexanedione 1.0 mmol), p-keto compound (3 2,4-pentadione or acetoacetate derivatives 1.0 mmol), ammonium acetate (4 1.0 mmol), and ceric ammonium nitrate (CAN) (0.05 mmol 5 mol%) followed by 0.5 mL of ethanol. The mixture was then stirred at room temperature until the reaction was completed as monitored by TLC (25 min to 7 h). The resulting reaction mixture was treated with brine solution followed by extraction with ethyl acetate (2 x 20 mL). After evaporation of the solvent, the crude yellow product was recrystalhzed from ethanol to give a yellow or brown solid in good to excellent yield (64-98%). All the products were characterized from their detailed spectral studies including NMR, NMR, EIMS and HRMS. 

Figure 7.20 illustrates an example of the methane/methyl iodide NlCl spectrum of 5,5-dimethyl-l,3-cyclohexanedione. In this example, methane is the [Ri] reagent gas that produces thermal electrons upon electron ionization. Methyl iodide is the [R2] reagent gas used to generate the reactive iodide anion ([ ] ) at m/z 127. This [I] anion reacts with 5,5-dimethyl-l,3-cyclohexanedione ([M] = 140 x) to produce the cluster [M+I] peak at m/z 267 (Reaction 7.14). Note there is no fragmentation for this NICI technique. 

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