Tetrahydrofuran ethers

Instmmental methods of analysis provide information about the specific composition and purity of the amines. QuaUtative information about the identity of the product (functional groups present) and quantitative analysis (amount of various components such as nitrile, amide, acid, and deterruination of unsaturation) can be obtained by infrared analysis. Gas chromatography (gc), with a Hquid phase of either Apiezon grease or Carbowax, and high performance Hquid chromatography (hplc), using siHca columns and solvent systems such as isooctane, methyl tert-huty ether, tetrahydrofuran, and methanol, are used for quantitative analysis of fatty amine mixtures. Nuclear magnetic resonance spectroscopy (nmr), both proton ( H) and carbon-13 ( C), which can be used for quaHtative and quantitative analysis, is an important method used to analyze fatty amines (8,81). 

The nature of the initiation step, which may occur in a variety of ways, is not known in all cases. Commonly used ethers such as ethyl ether, isopropyl ether, tetrahydrofuran, and i)-dioxane are particulady prone to form explosive peroxides on prolonged storage and exposure to air and light (see Peroxides AND PEROXY COMPOUNDS, ORGANIC), and should contain antioxidants (qv) to prevent their build-up. One of the exceptions to the peroxide forming tendency of ethers is methyl fert-alkyl ethers such as methyl fert-butyl ether [1634-04-4] (MTBE) and fert-amyl methyl ether [994-05-8] (TAME). Both have shown htde tendency if any to form peroxides (2,8). 

The hydroxy group can act as an intramolecular nucleophile. Solvolysis of 4-chlorobutanol in water gives as the product the cyclic ether tetrahydrofuran. The reaction is much faster than solvolysis of 3-chloropropanol under similar conditions. 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

Ethers — (R-O-R) are low on the scale of chemical reactivity. Aliphatic ethers are generally volatile, flammable liquids with low boiling points and low flashpoints. Well known hazardous ethers include diethyl ether, dimethyl ether, tetrahydrofuran. Beyond their flammability, ethers present an additional hazard they react with atmospheric oxygen in the presence of light to form organic peroxides. 

The isotopic purity of the products from a lithium aluminum deuteride reduction is usually equivalent to that of the reagent. The presence of moisture has little effect on the isotope composition of the products, causing only the decomposition of some of the reagent. For the best results, however, it is advisable to distill the solvent— usually ether, tetrahydrofuran or dioxane depending on the desired reaction temperature—from lithium aluminum hydride directly into the reaction flask. In this manner the reduction of 3-keto-5a-steroids (60), for example, gives the corresponding 3a-di alcohols (61) in 98% isotopic purity. ... 

The reaction can be performed under a variety of conditions. Origin-aiiyi2o,i26,234 acetylene and potassium in liquid ammonia were used. Subsequently, this was simplified by the use of potassium r-amylate in r-amyl alcohol and later this system was found to react selectively at C-17 in the presence of an A-ring a,j5-unsaturated ketone. A closer investigation of these reaction conditions revealed the formation of a small amount (2-3 %) of the disubstituted acetylene this can be avoided by reacting the 17-keto steroid with acetylenedimagnesium bromide in ether-tetrahydrofuran (see chapter 10.)... 

By reaction of an a-halo ester 1 with zinc metal in an inert solvent such as diethyl ether, tetrahydrofuran or dioxane, an organozinc compound 2 is formed (a Grignard reagent-like species). Some of these organozinc compounds are quite stable even a structure elucidation by x-ray analysis is possible in certain cases ... 

In small-scale experiments, overnight reaction of lithium dipropenylcuprate with lodobpnzene m ether containing 20 equivalents of pyridine at 25° gave 1-propenyl-benzene in 60 % yield. For couplmg with aromatic halides, this solvent system is superior either to ether-tetrahydrofuran or to ether containing 4 equivalents of hexamethylphosphonc triamide. 

Mobile phase n-Hexane - diisopropyl ether - tetrahydrofuran (85+10+5). Migration distance 5 cm Running time 16 min... 

List B contains all compounds that form peroxides which become dangerous when they reach a critical concentration. The danger will often become apparent during distillation operations. For hydrocarbons, this is the case for deca- and tetrahydronaphthalene, cyclohexene, dicyclopentadiene, propyne and butadiene. S ondary alcohols such as 2-butanol also form part of this list. Finally, for ethers there are diethyl ethers, ethyl and vinyl ethers, tetrahydrofuran, 1,4-dioxan, ethylene glycol diethers and monoethers. 

The equilibrium in this first step favors tlie shift to anhydride formation if the second mole of carboxylic acid in the second step with forms imidazole to form a salt that is insoluble in the solvent used (ether, tetrahydrofuran, benzene). 

This steam distillation removes ether, tetrahydrofuran, and other volatile neutral products. If too much water accumulates in the flask, it may be heated in an electric heating mantle after most of the ether has been removed. 

Peroxidizable hazard on concentration Diethyl ether Tetrahydrofuran Dioxane Acetal... 

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

Reaction of 4a-c with hydrogen chloride was carried out at room temperature in various solvents including dichloromethane, diethyl ether, tetrahydrofuran, acetonitrile, DMF, and l,l,l,3,3,3-hexafluoropropan-2-ol (HFIP). The ring opening of 4a-c readily proceeded to give the ester 10 as well as chloride substitution products, 8K and 9K, as shown in Scheme 8 (9). Product yields are dependent on the solvent, as summarized in Table II. Ester 10... 

The utility of these species as selective reducing agents has been thoroughly studied (29). Brown and McFarlin discovered that t-butyl alcohol reacts with LAH in a 3 1 molar ratio to give lithium tri-r-butoxyaluminum hydride (4, R = Bu1, n = 3) in ether, tetrahydrofuran (THF), or diglyme (30,31). The... 

EPOXYBUTANE METHYL ETHYL KETONE ETHYL VINYL ETHER TETRAHYDROFURAN cis-2-BUTENE-1,4-DIOL trans-2-BUTENE-1,4-DIOL ISOBUTYRIC ACID n-BUTYRIC ACID... 

Kumar, A. Temperature dependence of the densities and speeds of sound of the binary solutions of LiC104 with diethyl ether, tetrahydrofuran, acetone, and ethyl acetate, J. Chem. Eng. Data, 45(4) 630-635, 2000. 

Diethyl ether has been shown to enhance decarboxylation [32] as a secondary reaction after C—O bond cleavage when the ortho and para positions are blocked. Scheme 7 shows this effect for compound 17. Some esters with the ortho and para positions free to react but with bulky substiments at the meta position also undergo decarboxylation in ether, tetrahydrofuran, and dioxane [33,34],... 

Some of these heterocycles provide us with valuable laboratory solvents, e.g. the ethers tetrahydrofuran and dioxane (1,4-dioxane). Others are useful as organic bases, e.g. piperidine, pyrrolidine, and... 

Apart from the conversion of peroxides to useful products, it is sometimes necessary to reduce peroxides, and especially hydroperoxides formed by auto-oxidation. Such compounds are formed especially in hydrocarbons containing branched chains, double bonds or aromatic rings, and in ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, etc. Since most peroxidic compounds decompose violently at higher temperatures and could cause explosion and fire it is necessary to remove them from liquids they contaminate. Water-immiscible liquids can be stripped of peroxides by shaking with an aqueous solution of sodium sulfite or ferrous sulfate. A simple and efficient way of removing peroxides is treatment of the contaminated compounds with 0.4 nm molecular sieves [669]. 

The acylative cleavage of the cyclic ether tetrahydrofuran showed an excellent yield (95%) to 4-iodobutylbenzoate when fully acidic ionic liquid [EMIM]Al2Cl7 was used, but the yield to di-functionalized product (61%) suffered when the mildly acidic halogenoaluminate ionic liquid (which has a mole fraction of AICI3 (x) at a value of 0.52) was used as the solvent. In contrast, for 1,5-dimethyltetrahydrofuran and tetrahydropyran, a good yield to the cleavage products was obtained when the mildly acidic chloroaluminate was used. 

Lithium aluminum hydride is a flammable substance. It ignites spontaneously on grinding and reacts violently with water and many organic substances. Diethyl ether, tetrahydrofuran or another suitable solvent should be used in its synthetic applications. Dry or powdered limestone is an appropriate fire extinguishing agent. 

White orthorhombic crystals density 0.67 g/cm decomposes in moist air melts at 268°C decomposes at 380°C reacts with water dissolves in ether, tetrahydrofuran, and diethylamine solubility in ether, 25g/L at 25°C. 

Methyl fert-Butyl Ether MTBE Methyl Tertiary Butyl Ether Noncyclic Aliphatic or Aromatic Ethers Tetrahydrofuran Organophosphonates... 

Cyclohexene 2,3-dimethylbutene-2 2-butene dibutyl ether diisopropyl ether tetrahydrofuran 2-methyl THF. 

Wenn man Carbonsaure-nitrile bei — 78° mit Diisobutylalan in Pentan reduziert, das Pen-tan entfernt und den Riickstand bei — 78° mit Allyl- oder Benzyl-magnesiumchlorid bzw. mit Alkyl-lithium in Ether/Tetrahydrofuran umsetzt, erhalt man nach der hydrolytischen Aufarbeitung z. B. folgende Amine1. 

Diels-Alder reaction (Benzene, toluene, water, methanol, ethanol, diethyl ether, tetrahydrofuran, 1,4-dioxane, acetone, CHjCb, 1,2-dichloroethane, o-dichlorobenzene, chloroform, acetonitrile)... 

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