Aliphatic Ethers and Acetals

1 Aliphatic Ethers (and Acetals) The molecular ion peak (two mass units larger than that of an analogous hydrocarbon) is small, but larger sample size usually will make the molecular ion peak or the M + 

1 peak obvious (H- transfer during ion-molecule collision, see Section 2.4.1). 

The presence of an oxygen atom can be deduced from strong peaks at m/z 31, 45, 59, 73,. ... These peaks represent the RO+ and ROCH2+ fragments. Fragmentation occurs in two principal ways  

Cleavage of the C—C bond next to the oxygen atom (a, /3 bond, rule 8, Section 2.7) 

C—O bond cleavage with the charge remaining on the alkyl fragment. 

C—O bond cleavage with the charge remaining on the alkyl fragment. The spectrum of long-chain ethers becomes dominated by the hydrocarbon pattern. 

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The lower members of the homologous series of 1. Alcohols 2. Aldehydes 3. Ketones 4. Acids 5. Esters 6. Phenols 7. Anhydrides 8. Amines 9. Nitriles 10. Polyhydroxy phenols 1. Polybasic acids and hydro-oxy acids. 2. Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars) 3. Some amides, ammo acids, di-and polyamino compounds, amino alcohols 4. Sulphonic acids 5. Sulphinic acids 6. Salts 1. Acids 2. Phenols 3. Imides 4. Some primary and secondary nitro compounds oximes 5. Mercaptans and thiophenols 6. Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides 7. Some diketones and (3-keto esters 1. Primary amines 2. Secondary aliphatic and aryl-alkyl amines 3. Aliphatic and some aryl-alkyl tertiary amines 4. Hydrazines 1. Unsaturated hydrocarbons 2. Some poly-alkylated aromatic hydrocarbons 3. Alcohols 4. Aldehydes 5. Ketones 6. Esters 7. Anhydrides 8. Ethers and acetals 9. Lactones 10. Acyl halides 1. Saturated aliphatic hydrocarbons Cyclic paraffin hydrocarbons 3. Aromatic hydrocarbons 4. Halogen derivatives of 1, 2 and 3 5. Diaryl ethers 1. Nitro compounds (tertiary) 2. Amides and derivatives of aldehydes and ketones 3. Nitriles 4. Negatively substituted amines 5. Nitroso, azo, hy-drazo, and other intermediate reduction products of nitro com-pounds 6. Sulphones, sul-phonamides of secondary amines, sulphides, sulphates and other Sulphur compounds... 

Ethers, reactions of, 315, 671, 1067, 1068 see also under Aliphatic ethers and Aromatic ethers. p-Ethoxyphenylurea, 646 p-Ethoxyproptonitrile, 915,916 Ethyl acetate, 383 purificatioh of. 174 Ethyl acetoacetate, 475, 476, 477 keto-enol equilibrium of, 475, 1148 purification of, 478 reactions of, 478 ... 

Lithium bromide-Boron trifluoride etherate. Aliphatic ethers can be cleaved by reaction with lithium bromide and boron trifluoride etherate in acetic anhydride at room temperature for 30 hrs. Methoxycyclohexane, for example, is converted into a 7 1 mixture of acetoxycyclohexane and cyclohexene. Saturated steroid ethers are cleaved to mixtures of enes and acetates under these conditions choles-teryl methyl ether gave about equal parts of cholesteryl acetate and cholesteryl bromide. However, Narayanan reports that the lithium halide is not essential and indeed often detrimental. Thus cholesteryl methyl ether treated with boron trifluoride etherate and acetic anhydride in ether at 0° (14 hrs.) gave cholesteryl acetate in 93% yield. 

Similar treatment of oxygen-containing compounds, such as alcohols,203 aldehydes, acids, esters,197 ethers, and acetals, is almost always less successful than that of aliphatic hydrocarbons in most cases only chlorine, and no sulfur, enters the molecule. 

Catalytic hydrpgenation in acetic anhydride-benzene,- moves the aromatic benzyl ether and forms a monoacetate hydrogenation in ethyl acetate re-moves the aliphatic benzyl ether to give, after acetylation, the diacetate. ... 

The silica gel surface is extremely polar and, as a result, must often be deactivated with a polar solvent such as ethyl acetate, propanol or even methanol. The bulk solvent is usually an n-alkane such as n-heptane and the moderators (the name given to the deactivating agents) are usually added at concentrations ranging from 0.5 to 5% v/v. Silica gel is very effective for separating polarizable materials such as the aromatic hydrocarbons, nitro hydrocarbons (aliphatic and aromatic), aliphatic ethers, aromatic esters, etc. When separating polarizable substances as opposed to substances with permanent dipoles, mixtures of an aliphatic hydrocarbon with a chlorinated hydrocarbon such as chlorobutane or methylene dichloride are often used as the mobile... 

Additional acylation studies were also reported (24), (26). In the first case it is claimed that acylation of thiophene is achieved by means of HC104 and acetic anhydride affording a 65 % yield of 2-acetylthiophene. In the second paper Levine and coworkers reported that while 2,5-dimethylthiophene could be readily acetylated, 2,5-dichlorothiophene acetylated sluggishly. This is, however, readily explained, since the presence of chlorine atoms on the thiophene ring decreased its reactivity in electrophilic substitution reactions. In the case of methyl substitution, however, the 3 and 4 positions of the ring are activated toward electrophilic substitution by the inductive and hyperconjugative effects. Thus 2,5-dimethylthiophene was successfully acylated by the boron fluoride etherate method in high yield with three aliphatic anhydrides. 

On the other hand, the method of Mukaiyama can be succesfully applied to silyl enol ethers of acetic and propionic acid derivatives. For example, perfect stereochemical control is attained in the reaction of silyl enol ether of 5-ethyl propanethioate with several aldehydes including aromatic, aliphatic and a,j5-unsaturated aldehydes, with syir.anti ratios of 100 0 and an ee >98%, provided that a polar solvent, such as propionitrile, and the "slow addition procedure " are used. Thus, a typical experimental procedure is as follows [32e] to a solution of tin(II) triflate (0.08 mmol, 20 mol%) in propionitrile (1 ml) was added (5)-l-methyl-2-[(iV-l-naphthylamino)methyl]pyrrolidine (97b. 0.088 mmol) in propionitrile (1 ml). The mixture was cooled at -78 °C, then a mixture of silyl enol ether of 5-ethyl propanethioate (99, 0.44 mmol) and an aldehyde (0.4 mmol) was slowly added to this solution over a period of 3 h, and the mixture stirred for a further 2 h. After work-up the aldol adduct was isolated as the corresponding trimethylsilyl ether. Most probably the catalytic cycle is that shown in Scheme 9.30. 

Di- and tri-substituted enamines of aldehydes have been generated under mild conditions (1 h, 0°C, 1.2 equiv. of amine).278 Although easily isolable, they can be conveniently employed in situ. The reaction is chemoselective (ketones present are not affected), it tolerates sensitive groups such as acetals and silyl ethers, and it works for both aliphatic and aromatic aldehydes. 

DCA is the first bile acid whose inclusion ability was confirmed in the crystalline state. During the last century many research groups dealt with the inclusion compounds of DCA with various guest molecules, such as aliphatic, aromatic and alicyclic hydrocarbons, alcohols, ketones, fatty acids, esters, ethers, nitriles, peroxides and amines, and so on [2], In 1972, Craven and DeTitta first reported the exact crystal structure of DCA with acetic acid [3], Subsequent crystallographic studies made clear that most of DCA inclusion crystals have bilayer... 

Aliphatic primary silyl ethers are oxidized, probably via an aldehyde or acetal, to the simple esters formed from two equivalents of the silyl ethers (equation I). When a mixture of an aliphatic aldehyde and a primary silyl ether are oxidized under the... 

Hydroxymethylation of ketone (155) was followed by protection of the aliphatic hydroxy group (2-methoxypropyl ether) and addition of an a-benzyloxymethylene group at C-4. Acidic workup at the last stage of the reaction sequence produced (156). Its transformation to aldehyde (157) was carried out by successive treatment with methoxypropyl ether, acetic anhydride and pyridine, hydrochloric acid and methanol, and finally chromic acid, pyridine and hydrochloric acid. Dehydration of (157) led to the formation of (158) in 20% yield. Reagents other than the mentioned produced appreciable quantities of the cis A/B isomer. The butenolide (159) was finally synthesized by oxidation and hydrogenolysis. In order to complete the synthesis of triptolide it was necessary to introduce the... 

The degree of decomposition by the voltaic arc depends of course, to a great extent upon the chemical nature of the liquids and vapors in which the luminous arc is produced While ether, methyl alcohol, ethyl alcohol, glacial acetic acid, and other aliphatic fluids and their vapors are subject to decompositions with very trifling charring, and give products which are chemically closely related to the products started with, benzene, toluene, nitrobenzene, aniline, naphthalene, phenol, and other members of the aromatic series are destroyed, and considerable charring results. 

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