Opening of oxides


A facile method for the stereospecific labeling of carbon atoms adjacent to an oxygenated position is the reductive opening of oxides. The stereospecificity of this reaction is due to virtually exclusive diaxial opening of steroidal oxides when treated with lithium aluminum hydride or deuteride. The resulting /ra/w-diaxial labeled alcohols are of high stereochemical and isotopic purity, with the latter property depending almost solely on the quality of the metal deuteride used. (For the preparation of m-labeled alcohols, see section V-D.)  [c.204]

Cyclic compounds capable of undergoing ring opening (alkylene oxides, lactones, lactams, anhydrides, etc.).  [c.1014]

Tertiary alcohols are usually degraded unselectively by strong oxidants. Anhydrous chromium trioxide leads to oxidative ring opening of tertiary cycloalkanols (L.F. Fieser, 1948).  [c.136]

We saw an example of nucleophilic ring opening of epoxides in Section 15 4 where the reaction of Grignard reagents with ethylene oxide was described as a synthetic route to primary alcohols  [c.678]

As we ve just seen nucleophilic ring opening of ethylene oxide yields 2 substituted derivatives of ethanol Those reactions involved nucleophilic attack on the carbon of the ring under neutral or basic conditions Other nucleophilic ring openings of epoxides like wise give 2 substituted derivatives of ethanol but either involve an acid as a reactant or occur under conditions of acid catalysis  [c.681]

FIGURE 16 6 The mecha nism for the acid catalyzed nucleophilic ring opening of ethylene oxide by water  [c.682]

Cyproterone Acetate. Cyproterone, the free alcohol of cyproterone acetate, is an antiandrogen. Cyproterone acetate (41) is both an antiandrogen and a progestin. It is used in prostatic carcinoma treatment and for the control of Hbido. In females, it is used in conjunction with ethynylestradiol for the control of acne and hirsutism (65). Cyproterone acetate may be recrystallized from diisopropyl ether (66). It may be synthesized from 17-acetoxyprogesterone (42). The triene (67) reacts with diazomethane to give a pyrazoline pyrolysis, to effect loss of nitrogen, provides a cyclopropane (43) and oxidation with perbenzoic acid leads to an epoxide. Treatment with hydrochloric acid results in both the desired opening of the epoxide and the undesired cleavage of the cyclopropane. The cyclopropane is re-formed through treatment with coUidine to afford cyproterone acetate (41) (68-70).  [c.212]

Hydroxyprogesterone (39) has been prepared from (13). Treatment of (13) in alkaline hydrogen peroxide provided an epoxide. Opening of the epoxide is accompHshed by reaction with hydrogen bromide in acetic acid. Reductive removal of the bromide is performed in the presence of ammonium acetate, which prevents reduction of the double bond. The reaction mixture is heated with formic acid to provide the formate which is acylated. Subsequent Oppenauer oxidation (43) provides hydroxyprogesterone acetate (42). Saponification of the acetate with potassium hydroxide in methanol provides hydroxyprogesterone (39). This method is efficient in that direct oxidation of the formate avoids a deprotection step (93). Hydroxyprogesterone acetate (42) and hydroxyprogesterone caproate (59) also have been prepared from hydroxyprogesterone (39) (94).  [c.215]

Drying Characteristics. Alkyd reski molecules have a comblike stmcture, with a thermoplastic polyester backbone and dangling fatty acid side chains. Each fraction contributes to the drykig, or film-forming, characteristics of the reski. The backbone fraction dries by solvent release, similar to a lacquer material, whereas the side-chain fraction dries ki a manner similar to the oil from which the fatty acid came. Therefore, short oil alkyds develop a lacquer-type dryness relatively quickly due to faster solvent release, which is often further faciUtated by the fact that the solvents used have high volatihty. However, the through-dry derived from side-chain cross-linking is usually slower because the fatty acid side chains are fewer ki number and more scattered ki space, thus impeding cross linking with each other through the action of oxygen, and the dry surface impedes the transportation of ak oxygen down kito the film. On the other hand, long oil alkyds are relatively slow ki reaching the "set-to-touch" stage of surface drykig, but the greater abundance of fatty acid side chains and the relative openness of the film surface faciUtate the oxidative cross-linking reaction ki the film for reaching through-dry.  [c.32]

The reactions are highly exothermic. Under Uquid-phase conditions at about 200°C, the overall heat of reaction is —83.7 to —104.6 kJ/mol (—20 to —25 kcal/mol) ethylene oxide reacting (324). The opening of the oxide ring is considered to occur by an ionic mechanism with a nucleophilic attack on one of the epoxide carbon atoms (325). Both acidic and basic catalysts accelerate the reactions, as does elevated temperature. The reaction kinetics and product distribution have been studied by a number of workers (326,327).  [c.415]

Treatment of benzo derivatives with oxidizing agents leads to less predictable results. Thus, substituted 2,1-benzisoxazoles with nitrous acid or with CrOs/AcOH generated a variety of ring-opened products of higher oxidation state, the ratio of which depended on the amount of oxidant. These reactions are illustrated in Scheme 30.  [c.27]

Single-crystal technology has recently been adapted to do this, and has opened up the possibility of a new generation of ultra-compact high-speed devices. Figure 9.9 shows the method. A single-crystal wafer of silicon is first coated with a thin insulating layer of SiOj with a slot, or "gate", to expose the underlying silicon. Then, polycrystalline silicon ("polysilicon") is vapour deposited onto the oxide, to give a film a few microns thick. Finally, a capping layer of oxide is deposited on the polysilicon to protect it and act as a mould.  [c.95]

The catalytic method, as was shown in this study, has some advantages over arc-discharge tubule production. First, the yield of nanotubules in the catalytic production is higher than in the arc-discharge. It is possible to optimize the method for the deposition of almost all of the carbon in the form of tubular filaments. In the arc-discharge production the amount of tubules in the soot is usually no more than 25%. Isolation of nanotubules is also easier in the case of catalytic production. They can be separated from the substrate by the combination of various methods (ultra-sound treatment, chemical treatment). The high percentage of tubules in the product (only tubules are seen by TEM on the catalyst surface) makes possible their effective purification by gasification, either by oxidation or hydrogenation. The former treatment can also be used for the opening of nanotubules.  [c.25]

Fig. 4. Typical tip morphology obtained after high-temperature treatment (2000 °C) of oxidation opened CNTs. Note the elimination of dangling bonds by a bending of graphitic layer (marked with arrows). Fig. 4. Typical tip morphology obtained after high-temperature treatment (2000 °C) of oxidation opened CNTs. Note the elimination of dangling bonds by a bending of graphitic layer (marked with arrows).
The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.).  [c.50]

The now optically active epoxy acid was again stereoselectively bromolactonized, and the bro-tnine was removed with inversion and retention of configuration by tributyltin hydride. Reduction of the epoxide by catalytic hydrogenation and of the ketone using zinc borohydride led to a diol which was benzoylated and purified by crystallization. Methylation of the lactone introduced the last carbon atom at C-8 again stereoselectively from the a-side of the bicycHc system. Base-catalyzed opening of the lactone and Jones oxidation of the alcohol yielded a protected cyclohexanone derivative with all substituents in the correct positions. Baeyer-Villiger oxidation and treatment with 2,2 -dipyrklyl disulfide concluded the synthesis of fragment (A). It contains a good leaving group at C-9 which could be substituted by a carbanionic fragment (B).  [c.319]

A smoother ring opening of 2-aminothiazoles (and A-2-thiazolines) occurs with transition metal salts such as (PtCl4) " or (PdiCU) " in basic medium (Scheme 99) (486). Finally, alkaline ring cleavage of thiazolium salts is a classical reaction of this class of compounds and is discussed in Chapter IX. Thiazoie ring opening resulting from photosensitized oxidation of thiazoles has been discussed in Section IIL7.A.  [c.136]

A third example is the industrial preparation of ethylene glycol (HOCH2CH2OH) by hydrolysis of ethylene oxide in dilute sulfuric acid This reaction and its mechanism (Figure 16 6) illustrate the difference between the ring openings of epoxides discussed m the preceding section and the acid catalyzed ones described here Under conditions of acid catalysis the species that is attacked by the nucleophile is not the epoxide itself but rather its conjugate acid The transition state for ring opening has a fair measure of carbocation character Breaking of the ring carbon-oxygen bond is more advanced than formation of the bond to the nucleophile  [c.681]

Examination of the stmctures of the alkaloids (17) obtained from Cinchona suggests that they probably have a different pattern of formation than those already discussed. However, the differences are more formal than profound. Thus the l-a2abicychc system is formed from one of the aldehyde equivalent carbons of a secologanin (102) bound fragment with the terminal nitrogen of tryptamine (98, R = H). Cleavage of that nitrogen away from the indole leaves behind the carbon to which it was bound, formally, at the oxidation level of an aldehyde. Then, oxidative opening of the ftve-membered ring between the indole nitrogen and the adjacent carbon is followed by recycli2ation from the aryl amine so Hberated to the aldehyde function set free in the previous step. Thus the nine expected carbons, one of the original carbons in the C q fragment having been lost by decarboxylation, remain.  [c.551]

Monopropylene glycol (1,2-propanediol) is a difiinctional alcohol with both a primary and a secondary hydroxyl. Chemically, the presence of the secondary hydroxyl group differentiates propylene glycol from ethylene glycol, which has two primary hydroxyl groups. Coproducts dipropylene glycol and tripropylene glycol have several possible stmctural and stereochemical isomers. Examination of the mechanisms for addition of an alcohol to an oxirane ring under various reaction conditions explains the distribution of the various isomers in the product mix (7). In the high pressure, high temperature process for hydrolysis of propylene oxide to propylene glycol and the subsequent formation of dipropylene and tripropylene glycol, the neutral to slightly acidic conditions dictate a nonspecific opening of the oxirane ring. The nonspecific nature of the acid-cataly2ed reaction is seen in the approximately 50 50 product distribution for the primary to secondary alcohol isomers in the dipropylene glycol produced in the process. In the base-cataly2ed propoxylation of an alcohol, for example in poly(propylene glycol) manufacture, attack is at the less substituted position of the oxirane ring, leading to the preferential formation of the secondary alcohol.  [c.366]

Oxidative Ring Opening. Many oxidizing reagents, such as peracids, ozone [10028-15-6] or Fel2, are suitable for oxidative deamination of aziridines to give olefins (18). On the other hand, oxidation of bicycHc 2,3-polymethyleneaziridines with lead tetraacetate leads to retention of the nitrogen ia the molecule with the formation of CO-keto nitriles (338).  [c.11]

The all-cis tetrahydrofuran ring of goldinamine was synthesized by the consecutive epoxide opening of the ester enolate derived from (42) according to an old concept as shown in Figure 4 (61). The five adjacent stereocenters in (42) were assembled by a kinetic resolution of alcohol (38) via its epoxide (39). One of the newly gained stereocenters was sacrificed to gain the aHyUc alcohol (40) which was subjected to a Sharpless epoxidation to introduce the third stereocenter. An epoxidation of the homoaHyhc alcohol (41) using y -chloroperbenzoic acid generated the two additional stereocenters with a diastereoselectivity of 94%. Hydrogenolysis of the benzyl ether, hydrolysis of the silyl ether, protection of the resulting diol, and oxidation of the primary alcohol gave a carboxyUc acid which, after deprotonation, generated an alkoxide ion that opened the terminal epoxide to furnish the desired tetrahydrofuran (43). Further elaboration via (44) and (45) gave the terminal alkene (46) which was subjected to a stereoselective hydroboration to introduce the fifth consecutive stereocenter. A Swem oxidation of the resulting alcohol, followed by reaction with lithium di(a-methoxyvinyl)cuprate, led to the vinyl ether (48), the hydrolysis of which gave (49) with the sixth stereocenter in 73% de. A Wittig-Horner reaction using trimethyl phosphonoacetate estabUshed the (E)-geometry of the alkene with a stereoselectivity of 78%. An additional reduction step led to aldehyde (50).  [c.525]

OtherPoIya.Idehydes, A number of dialdehyde reagents can be prepared by oxidizing the ring stmctures of sugars or nucleotides (116). These reagents can react with hemoglobin at any of its amino groups and therefore form a variety of modifications including intramolecular and intermolecular links. One example of this type of modification involves opening the ring of inositol tetraphosphate. Another example, involves the opening of the pyridine ring of ATP (117) to form modified ATP—hemoglobin. This latter product was reported to have an elevated P q and normal cooperativity.  [c.166]

Colloidal Solids. Used as reinforcement agents ia metals, ceramics, and polymers (136,137), particles of coUoidal solids may be spherical, angular, fibnUar, or flake-shaped. Examples iaclude alumina and thoria to reinforce aluminum and nickel, respectively, by providing obstacles to the movement of dislocations ia the metals, and zUconia and sUicon carbide to reinforce a variety of ceramics, eg, alumina, sUicon nitride, and glass, by inhibiting the propagation and opening of cracks ia the matrix (see Composite Materials). Asbestos, crystalline sUicas, and organic solids are added to concrete to improve its strength by providing an interlocking particulate stmcture within the concrete matrix (139) asbestos (qv) (140), various oxides (141), and carbon black (27,141) are added to reinforce polymers by inducing a stiffened or high yield matrix. For instance, maximum strength of natural mbbermaybe achieved with - 10 vol % ZnO or -- 22 vol % carbon black (qv) and that of TD (thoria-dispersed) nickel by -- 3 vol % Th02 (136).  [c.400]

Engineering thermoplastics are priced between the very expensive resins and the high volume, low priced commodities, eg, poly(phenylene oxide)—polystyrene alloys at 2/kg to polyetheretherketones at 60/kg (Fig. 1). Many specialty and commodity resins are addition polymers. Their prices are primarily governed by raw material costs and the complexity of the manufacturing process. Thus the raw material for fluoropolymers is much more expensive than the olefins used for polyethylenes (PE), polystyrenes (PS), acryUcs, vinyl chloride polymers, etc. Engineering polymers tend to be composed of aromatic monomers, except for acetals and nylons, and their monomers are usually linked by condensation (ester, carbonate, amide, knide), substitution (sulfide) or oxidative coupling (ether), and in a few cases, addition (polyolefins). High monomer costs and complex polymerisation processes force higher prices (12). Larger volumes of production take advantage of economy of scale. Representative producers and trademarks of engineering plastics are given in Table 2. Key producers include multinational companies, with plants in many countries. Recent pohtical events such as the opening of Eastern Europe, the North American Free Trade Zone, the advancing European Economic Union, and sharpening competition are increasing the multinational efforts to seek local pricing advantages by use of cheaper local labor, elimination of transport charges, and local tax incentives.  [c.262]

With W-substituted quaternary derivatives in the presence of oxidizing agents, ring opening is avoided and the classical Dekker oxidation of the pseudo-base occurs to give (45) (62JCS1671).  [c.208]

The nitrosation of pyrroles and indoles is not a simple process. The 3-nitroso derivatives (84) obtained from indoles exist largely in oximino forms (85) (80IJC(B)767). Nitrosation of pyrrole or alkylpyrroles may result in ring opening or oxidation of the ring and removal of the alkyl groups. This is illustrated by the formation of the maleimide (86) from 2,3,4 -trime thylpyrrole.  [c.56]

Oxidation to an azolone is an expected reaction for a pseudo base, but little appears to be known of such reactions. Most commonly, pseudo bases suffer ring fission. Estimated rates of ring-opening of (169) are in the ratio 10 10" 1 for X = O, S and NMe, respectively (79AHC(25)1).  [c.63]

Ozone is reported to yield a sulfoxide from norbornene episulfide (74JAP7435375), but its gas phase reaction with thiirane gives sulfur dioxide, ethylene, formaldehyde and carbon dioxide (80MI50600). Nitric acid and potassium permanganate give extensive oxidative ring opening of thiirane, carboxysulfonic acids being isolated in the reaction with nitric acid.  [c.151]

The thermal stability of the silicone matrix reflects the stability of the polysilox-ane polymers. Thus, in the absence of catalyst residue, silanol groups, and moisture, depolymerization, moleeular rearrangement, and erosslinking reaetions are reduced. The depolymerization of PDMS in vacuum or in inert atmospheres starts in the range of 220°C and leads to the formation of oligomeric cyclosiloxanes. Continuous heating at 350°C will lead to complete degradation, due in part to depolymerization and in part to rearrangement. These limits in temperature degradation suggest an upper use temperature of 200°C for adhesive joints exposed continuously to thermal radiation, and around 300°C for short time exposures. The permeability of silieones to oxygen is very high, which opens the possibility of oxidative degradation mechanisms operating on the organic side chains. Therefore, when the adhesive is continuously exposed to air the upper temperature limit is set to 160°C.  [c.699]

The gasification of graphite layers proceeds more easily at the tips of the tubules and at structural defects. Typical images of the tips of catalytically produced tubules after treatment in air are presented in Fig. 11. On graphite tubules grown from Co-Si02 catalyst, two types of tip were usually observed. In the first, the tubules are closed by graphite layers with the metal particle inside the tubules (Fig. 4(a)). In the second type, more generally observed, the tubules are closed with amorphous carbon. The opening of tubules during oxidation could proceed on both types of tip.  [c.24]

The and -methylmorphimethines (formula, p. 251) are catalytically hydrogenated to hexahydro-derivatives by saturation of the two ethylenic linkages and opening of the oxide ring. The one from the e-form has m.p. 155° and that given by the -form, m.p. 174-5° (Speyer and Koulen ).  [c.252]

Reductive opening of the cyclopropyl ring in 9j5,19-cycloandrostan-ll-one (234) has been achieved by treatment with a large excess of sodium in iso-propanol-OD. Analysis of the product for isotopic purity after oxidation to the corresponding ketone and base-catalyzed back exchange of the 9a-deuterium [(235) (236)] shows 19% do and 10% 62 isotopic impurities. The 10% 62 product is probably due to incomplete back exchange.  [c.206]

Among the reactions of this general category, the rearrangement of a,j5-epoxy ketones to j5-dicarbonyl isomers has found the widest application in the steroid field due to the work of Jeger, Schaffner and co-workers. Irradiation of the 3-oxo-4,5-oxido steroids (70) and (71) leads to opening of the oxide ring and (5 4)-rearrangement to yield a single enolized ] -diketone (72) from both stereoisomers. Some of these 10(5 4)-fl eo-3,5-diketones exhibit remarkable anabolic activity [e.g., 17 -hydroxy-7a,17-dimethyl-10(5 4)-flZ eoestrane-3,5-dione (82)]. The stereoisomeric methyl homo-logues (73) and (75) give, in each case, a single product [(74) and (76), respectively] which differ only in their configuration at C-4.  [c.307]

This interesting phenomenon has been explained by the tunnelling of electrons from localised states at a tip with energies close to the Fermi energy, stimulated by the enhancement of the electric field from their ID structure [38]. Based on the Fowler-Nordheim model (Fig. 13 inset), it was calculated that the electric field at the tip is enhanced about 1300 times [38], but there is some discussion on the validity of this model [44]. The model that electrons are emitted from single atomic wires protruding from the tips of CNTs [41] is still hypothetical and has not been confirmed. It is very interesting to note that the opening of tips by oxidation with either oxygen-plasma treatment or by heating in oxygen-gas makes CNTs more highly emissive [41,45]. Considering the hollow image of emission of open-tip MWCNTs shown in Fig. 14 [46], the emission from almost all the carbon atoms around the tip is plausible.  [c.176]

Fluoride ion can also initiate ring opening of hexafluoropropylene oxide to give a heptafluoropropoxide, which can react in turn with the epoxide to give dimers or higher oligomers that are precursors to perfluorinated stable fluids [277, 27S, 279] (equation 61).  [c.83]

Sephadex is insoluble in all solvents that do not chemically degrade the cross-linked dextran. However, the gel may shrink or swell in the presence of organic solvents, which will impact the porosity of die gel and hence the selectivity. Shrinkage of Sephadex in ethanol is used for producing stable beds by a special packing procedure. Dextran, like most carbohydrates, may be subject to chemical modifications such as methylation, amination, carboxyla-tion, or sulfonation at the reducing end of the polymer or at various hydroxyl groups along the polymer. Although many of the reactions have been used to introduce various ligands to Sephadex for adsorptive chromatographic applications, the strongly oxidative conditions required to derivitize dextrans should be avoided when using Sephadex. Although stable over the pH range of 2 to 10, the prolonged exposure of Sephadex to strongly acidic or basic conditions may cause hydrolysis of the gel by disruption of the glycosidic linkages or ring opening of the component glucose residues. However, exposure of Sephadex to 0.1 M HCl or 0.1 M NaOH for 2 hr or storage in 0.02 M HCl for 6 months showed no effect on chromatographic performance. Sephadex may be used at elevated temperatures and may even be autoclaved at 120 C for 30 min without affecting chromatographic performance. Above 120°C, Sephadex may begin to caramelize. Freezing and thawing of hydrated Sephadex may result in disruption of the bead structure and should be avoided.  [c.39]


See pages that mention the term Opening of oxides : [c.204]    [c.188]    [c.308]    [c.320]    [c.91]    [c.152]    [c.159]    [c.238]    [c.417]   
See chapters in:

Organic reactions in steroid chemistry  -> Opening of oxides