Reaction procedure

The product is washed with two 0.5-mL portions of cold water. 

The benzoin produced in this experiment contains a chiral carbon atom (a stereocenter), but the product itself is not optically active. Explain. 

The cyanide ion is a highly specific catalyst for the benzoin condensation. Can you list three functions this ion performs in this catalytic role  

Can you suggest a reason why p-cyanobenzaldehyde does not undergo the benzoin condensation to yield a symmetrical benzoin product  

Tollens reagent is used as a qualitative test for the presence of the aldehyde functional group (see Chapter 9, Classification Tests). However, benzoin, which does not contain an aldehyde, gives a positive test with this reagent. Explain. 

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Aldol Addition and Related Reactions. Procedures that involve the formation and subsequent reaction of anions derived from active methylene compounds constitute a very important and synthetically useful class of organic reactions. Perhaps the most common are those reactions in which the anion, usually called an enolate, is formed by removal of a proton from the carbon atom alpha to the carbonyl group. Addition of this enolate to another carbonyl of an aldehyde or ketone, followed by protonation, constitutes aldol addition, for example... 

The polyimide shown is a tme thermosetting resin, but the general reaction procedure, coupling the dianhydride with the diamine, is extremely important throughout polyimide chemistry. The intermediate polyamic acid polymers form the basis for many of the polyimide resins used in advanced composites. 

This reaction procedure has also been used for the synthesis of oxazolo[3,2-fl]pyridine and imidazo[l,2-fl]pyridine derivatives, and the numerous variations studied, allowing changes of the substituent pattern and the number and position of the nitrogen atoms in the six-membered ring, are described in Chapters 4.10 and 4.29. 

The general reaction procedure and apparatus used are exactly as described in Procedure 2. Ammonia (465 ml) is distilled into a 2-liter reaction flask and to this is added 165mlofisopropylalcoholandasolutionof30g(0.195 mole) of 17/ -estradiol 3-methyl ether (mp 118.5-120°) in 180 ml of tetrahydrofuran. The steroid is only partially soluble in the mixture. A 5 g portion of sodium (26 g, 1.13 g-atoms total) is added to the stirred mixture and the solid dissolves in the light blue solution within several min. As additional metal is added, the mixture becomes dark blue and a solid (matted needles) separates. Stirring is inefficient for a few minutes until the mass of crystals breaks down. All of the sodium is consumed after 1 hr and 120 ml of methanol is then added to the mixture with care. The product is isolated as in Procedure 4h 2. After being air-dried, the solid weighs 32.5 g (ca. 100% for a monohydrate). A sample of the material is dried for analysis and analyzed as described in Procedure 2 enol ether, 91% unreduced aromatics, 0.3%. The crude product may be crystallized from acetone-water or preferably from hexane. 

A detailed reaction procedure is not available. The reaction fails with (CH3)aCuLi/Tt20 and CH,Li/ CeC 1,/THF. 

The catalyst prepared above was characterized by X-ray diffraction, X-ray photoelectron and Mdssbauer spectroscopic studies. The catalytic activities were evaluated under atmospheric pressure using a conventional gas-flow system with a fixed-bed quartz reactor. The details of the reaction procedure were described elsewhere [13]. The reaction products were analyzed by an on-line gas chromatography. The mass balances for oxygen and carbon beb een the reactants and the products were checked and both were better than 95%. 

In 2001, we developed a simple and quite useful method to manipulate the size of Au nanoparticles by using the heat-treatment of small Au nanoparticles [9,10], which is far from the conventional techniques. The 1-dodecanethiol-protected Au nanoparticles (C12S-AU) of 1.5 0.2 nm in size synthesized by the Brust s two-phase (toluene/water) reaction procedure [3] were heat treated at 150-250 °C at the heating rate of 2°Cmin and held for 30min. This heat treatment of as-synthesized C12S-AU nanoparticles... 

The synthesis of C S-Au nanoparticles as a source for the heat treatment followed the Ernst s two-phase (toluene/water) reaction procedure [3]. The organic (toluene) phase was then separated, evaporated completely in a rotary evaporator at 40 °C, and dried in vacuo at 30 °C for a day. The crude solid obtained was heat treated at 150-250 °C at the heating rate of 2°Cmin, and held for 30 min. The heat-treated product was dissolved in toluene and mixed with methanol to remove excess free C12SH and TOAB. The dark brown precipitate... 

Cyclization to six-membered rings (Eq. 15) provided modest diastereoselectivity and required the use of bulkier PhMeSiH2 to prevent olefin hy-drosilylation. Propargyl and homopropargyl amines 94 afforded a variety of heterocycles (Scheme 21), if the catalyst was added slowly over the reaction course to diminish side reactions resulting from metal coordination to the basic amine [56]. The reaction procedure was extended to the diastereoselect-ive bicyclization of dienyne substrate 95, giving 96 as product in a cascade fashion (Eq. 16) [57]. 

Scheme 1.29. Domino acyliminium ion cyclization/Ritter reaction procedure in the synthesis of CPG 49823 (1-116).

The heterofunctional linking approach, in spite of its potential efficiency, has not been yet explored for the synthesis of //-stars. A reaction procedure is given in Scheme 89. Living PDMS is selective only for Si - Cl groups. The... 

Later it was shown in reactions of aromatic aldehyde methylhydrazones 137a-f with benzonitrile oxide that the initially formed Z-adduct 138, depending on the reaction procedure and the substituents, undergoes either isomerization to the thermodynamically stable E-adduct 139, tautomerization to an oxatriazine 140 or irreversible cyclization to a triazole 141 (Scheme 1.28). The structure of 4-methyl-3.6-diphenyl-5,6-dihydro-4//-1,2.4,5-oxatriazinesl40a was confirmed by an X-ray study (308). 

An alternative to the synthesis of epoxides is the reaction of sulfur ylide with aldehydes and ketones.107 This is a carbon-carbon bond formation reaction and may offer a method complementary to the oxidative processes described thus far. The formation of sulfur ylide involves a chiral sulfide and a carbene or carbenoid, and the general reaction procedure for epoxidation of aldehydes may involve the application of a sulfide, an aldehyde, or a carbene precursor as well as a copper salt. This reaction may also be considered as a thiol acetal-mediated carbene addition to carbonyl groups in the aldehyde. 

This preparation may be accomplished by using one molecular equivalent of lithium amide special reaction procedures must be employed, however, and the yields are not reproducible.2 The preparation may also be accomplished (with reduced yield) by using sodium amide, but only under special reaction conditions.3... 

In contrast to the conjugated system, the reactivity of hexahydro-isoxazolo[2,3-tf] pyridines has been the subject of considerably more attention, which can most certainly be attributed to its greater synthetic potential, as demonstrated by the synthesis of many complex natural products. However, most of the reactions reported since 1996 have been known for many years and the last decade was in fact characterized by their use in syntheses or optimization. After a brief survey of the thermal reactions, procedures involving the reductive cleavage of the N-O bond will be detailed. 

Wagner et al. used the reaction procedure shown in Fig. 4.2.5, and variations thereof, to yield the monodisperse oligoethoxylate monomethyl ether oligomers (n = 3-9). The trisiloxanes were then produced by hydrosilylation as in step b of Fig. 4.2.4 [72]. Distillation procedures were used to purify the intermediates and resulting trisiloxane alkylethoxylate products, and structural characterisation was performed by GC-MS and NMR. Purities for the n = 3-9 oligomers of 99, > 99, 99, 97.5, 96, 95 and 90%, respectively, as determined by GC-MS, were reported. 

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