Initial addition

Place 8 0 g. of magnesium turnings or ribbon and 80 ml. of the dry benzene in the flask. Prepare a solution of 9-0 g. of mercuric chloride in 50 ml. of the dry acetone, transfer it to the dropping-funnel, and then allow it to enter the flask slowly at first, and then more rapidly, so that the addition takes about 3-5 minutes. The reaction usually starts shortly after the initial addition of the mercuric chloride solution if it is delayed, it may then start vigorously, and the flask may have to be cooled in water to prevent escape of acetone through the condenser. 

As in most electrophilic reactions, the abiUty to stabilize the positive charge generated by the initial addition strongly affects the relative rates. MX reacts faster than OX and PX because both methyl groups work in conjunction to stabilize the charge on the next-but-one carbon. Sulfonation was, at one time, used to separate MX from the other Cg aromatic isomers. MX reacts most rapidly to form the sulfonic acid which remains in the aqueous phase. The sulfonation reaction is reversible, and MX can be regenerated. 

Fig. 1. Bulk polymerization of diethylene glycol bis(aHylcarbonate) at 45°C with initial addition of 3.0% diisopropyl percarbonate. Rates of polymerization as measured by density and catalyst consumption decrease with time at a given temperature (14).

Ethoxylation and Propoxylation. Ethylene oxide [75-21-8] or propylene oxide [75-56-9] add readily to primary fatty amines to form bis(2-hydroxyethyl) or bis(2-hydroxypropyl) tertiary amines secondary amines also react with ethylene or propylene oxide to form 2-hydroxyalkyl tertiary amines (1,3,7,33—36). The initial addition is completed at approximately 170°C. Additional ethylene or propylene oxide can be added by using a basic catalyst, usually sodium or potassium hydroxide. 

Recognition of the thio group s key role in biochemistry has led to studies of l,4-ben2oquinone with glutathione, a tripeptide 7-Glu-Cys-Gly (GSH). The cross-oxidation of the initial addition product by excess quinone leads, under physiological conditions, to all three isomeric products (46), ie, the 2,3-and 2,6-isomers as well as the 2,5-disubstituted l,4-ben2oquinone shown. 

The length of the zone and the diameter of the tod are chosen in such a way that surface tension and interactions between circulating electric currents in the molten zone and the radio-frequency (r-f) field from the surrounding induction coil keep the molten zone in place. As of this writing (ca 1996), the maximum sihcon rod diameter that can be purified in this manner is ca 125 mm. Initially, additional purification can be obtained by making mote sweeps of the zone. Eventually, however, more sweeps do not remove any additional impurities. The limiting profile is given by equation 4 ... 

Scaling is not always related to temperature. Calcium carbonate and calcium sulfate scaling occur on unheated surfaces when their solubiUties are exceeded in the bulk water. Metallic surfaces are ideal sites for crystal nucleation because of their rough surfaces and the low velocities adjacent to the surface. Corrosion cells on the metal surface produce areas of high pH, which promote the precipitation of many cooling water salts. Once formed, scale deposits initiate additional nucleation, and crystal growth proceeds at an accelerated rate. 

The conjugated stmcture of 1,3-butadiene gives it the abiUty to accept nucleophiles at both ends and distribute charge at both carbon 2 and 4. The initial addition of nucleophiles leads to transition states of TT-ahyl complexes in both anionic and transition-metal polymerizations. 

In the isomeric 2,1-benzisoxazole series halogenation also occurs in the 5-position, but it appears that an initial addition product is formed at the 4,5-positions (67AHC(8)277, p. 321). 

Cycloadditions of aziridines to diphenylcyclopropenone lead to 4-oxazolines (36) (70CJC89). A mechanism involving initial addition to the cyclopropenone carbonyl group followed by ring opening and recyclization was suggested. 

Careful watching is necessary at this point, since if the distillation is carried too far a violent reaction, apparently a rearrangement of the initial addition product may set in. 

In a simple free-radical-initiated addition polymerisation the principal reactions involved are (assuming termination by combination for simplicity)... 

Over the years many blends of polyurethanes with other polymers have been prepared. One recent example is the blending of polyurethane intermediates with methyl methacrylate monomer and some unsaturated polyester resin. With a suitable balance of catalysts and initiators, addition and rearrangement reactions occur simultaneously but independently to give interpenetrating polymer networks. The use of the acrylic monomer lowers cost and viscosity whilst blends with 20% (MMA + polyester) have a superior impact strength. 

The /rans-fiised decalin system is conformationally rigid, and the stereochemistry of the product indicates that the initial addition of the trichloromethyl radical is from the axial direction. This would be expected on stereoelectronic grounds, because the radical should initially interact with the n orbital. The axial trichloromethyl group then shields the adjacent radical position enough to direct the bromine abstraction in the trans sense. 

Nonetheless, the reduction clearly proceeds by initial addition of one electroi to the aj omatic ring and the resulting radical-anion must be protonated ii some way before the second electron addition can occur. 

When acetic anhydride is used in the CF3CCI3 and zinc reaction with aldehydes, the initial addition product undergoes an elimination reaction to give 2-chloro-l,l,l-trifluoro-2-alkenes exclusively [60, 63] (equation 51)... 

Fluoride ion produced from the nucleophilic addition-elimination reactions of fluoroolefins can cataly7e isomerizations and rearrangements The reaction of per fluoro-3-methyl-l-butene with dimethylamine gives as products 1-/V,/Vdimeth-ylamino-1,1,2,2,4,4,4-heptafluoro-3-trifluoromethylbutane, N,W-dimetliyl-2,2,4,4,4-pentafluoro 3 trifluoromethylbutyramide, and approximately 3% of an unidentified olefin [10] The butylamide results from hydrolysis of the observed tertiary amine, and thus they share a common intermediate, l-Al,A -dimethylamino-l,l 24 44-hexafluoro-3-trifluoromethyl-2-butene, the product from the initial addition-elimination reaction (equation 4) The expected product from simple addition was not found... 

Examples of perfluoroalkyl iodide addition to the triple bond include free radical addition of perfluoropropyl iodide to 1 -heptyne [28] (equation 21), thermal and free radical-initiated addition of lodoperfluoroalkanesulfonyl fluorides to acetylene [29] (equation 22), thermal addition of perfluoropropyl iodide to hexa-fluoro 2 butyne [30] (equation 23), and palladium-catalyzed addition of per-fluorobutyl iodide to phenylacetylene [31] (equation 24) The E isomers predominate in these reactions Photochemical addition of tnfluoromethyl iodide to vinylacetylene gives predominantly the 1 4 adduct by addition to the double bond [32] Platinum catalyzed addition of perfluorooctyl iodide to l-hexyne in the presence of potassium carbonate, carbon monoxide, and ethanol gives ethyl () per fluorooctyl-a-butylpropenoate [JJ] (equation 25)... 

When acetone is treated with hydroxylamine in aqueous solution near neutral pH, the carbonyl UV absorption intensity decreases very rapidly this fast spectral change is followed by a much slower absorption increase that is due to the appearance of the oxime product. This suggests that, at such pH values, the initial addition is very rapid and the second step, dehydration of the carbinolamine, is the rds. Figure 5-12 is a plot of the apparent first-order rate constant against pH for this reaction. As the pH is decreased from neutrality, the rate increases, indicating that the rds... 

However, as the pH—rate plot shows, at very low pH the observed rate actually decreases. Because, as the preceding argument shows, rate-determining dehydration should result in a pH-dependent rate at low pH, this decreased rate must mean that the rds has changed. This is reasonable, for at pH values well below the pKg of hydroxylamine, the decreasing proportion of the hydroxylamine in the unprotonated form will decrease the rate of the initial addition. At some pH, then, the rate of the addition step will fall below that of the dehydration step, and the observed rate curve will lie lower than the rate predicted for the dehydration. 

At which point in the initial addition is there the greatest separation of charge Draw Lewis structures for C4H9 and Cl that show all nonbonding electrons and formal charges. 

The first representatives of this group of compounds, 1,5-benzotelluroazepinones 57, have been prepared in 17% yield by the reaction between 2-iodopropyolanilides and NaHTe (98H631). The reaction proceeds, most probably, as nucleophilic substitution of the iodine, resulting in telluroles 58 and the subsequent nucleophilic addition of a hydrotelluride group to the triple bond. An alternative mechanism involving initial addition of NaTeH to the triple bond followed by the nucleophilic substitution of the iodine atom was mled out because the anilides PhNHCOC=CR do not react with NaTeH under the conditions at which the heterocycles 57 were obtained. Neither of the adducts PhNHCOCH=C(R)TeH or [PhNHCOCH=C(R)Te]2 was isolated. 

The foregoing examples do not represent useful chiral formyl anion equivalents in a direct sense since the stereoselectivity of the initial addition to aldehydes is poor, although as has been explained, the situation is salvaged by oxidation and re-reduction. On the other hand, by lithiation at the 2 position of the achiral oxazo-lidine 53 in the presence of (-)-sparteine followed by addition of benzaldehyde, useful levels of d.e. and e.e. are achieved directly (98TA3125). For example, by adding MgBr2 before the benzaldehyde, the major product obtained is 54 in 80% d.e. and 86% e.e. 

The reaction of benzyl radicals wdth several heterocyclic compounds W as more extensively studied by Waters and Watson, " - who generated benzyl radicals by decomposing di-tert-butyl peroxide in boiling toluene. The products of the reaction with acridine, 5-phenyl-acridine, 1 2- and 3 4-benzacridine, and phenazine were studied. Acridine gives a mixture of 9-benzylacridine (17%) (28) and 5,10-dibenzylacridan (18%) (29) but ho biacridan, w hereas anthracene gives a mixture of 9,10-dibenzyl-9,10-dihydroanthracene and 9,9 -dibenzyl-9,9, 10,10 -tetrahydrobianthryl. This indicates that initial addition must occur at the meso-carbon and not at the nitrogen atom. (Similar conclusions were reached on the basis of methylations discussed in Section III,C.) That this is the position of attack is further supported by the fact that the reaction of benzyl radicals with 5-... 

CN/CC replacement has also been observed on treatment of pteridine with malonitrile or cyanoacetamide 6-amino-7-R-pyrido[2,3,-h]pyrazine (R = CN, CONH2) beingformed (73JCSP(1)1615) (Scheme 15). The reaction involves initial addition of the reagent to the N-3-C-4 bond, scission of the dihydro bond between N-3 and C-4 in the covalent adduct, and recycli-zation. This mechanism is fundamentally different from the mechanism mentioned in Scheme 14, where two molecules of the reagent were used for addition and where the bond breaking takes place between N-1 and C-2. 

In alkaline solution, the phenol 1 is deprotonated to the phenolate 4, which reacts at the ort/zo-position with dichlorocarbene 3. The initial addition reaction product 5 isomerizes to the aromatic o-dichloromethyl phenolate 6, which under the reaction conditions is hydrolyzed to the o-formyl phenolate." ... 

Interposition of a methylene group between the phenyl ring and the heterocycle leads to the benzyldiami nopyrimidines, a class of compounds notable for their antibacterial activity. Condensation of hydrocinnamate 54 with ethyl formate leads to the hydroxymethylene derivative 55. In this case, too, the heterocyclic ring is formed by reaction with guanidine. This sequence probably involves initial addition-elimination to the forniyl carbon to form 56 cyclization in this case involves simple amide formation. Tautomerization then affords the hydroxy derivative 57. This is converted to tetroxoprim (58) by first... 

At present, high-temperature stabilization of polyolefins is still misunderstood besides, this problem presents serious difficulties. Stabilization of thermal oxidation and photoinduced destruction with the use of stabilizers in this case is inefficient, since at high temperatures these stabilizers are easily evaporated out of the polyolefin melt and decomposed with the formation of radicals capable of initiating additional kinetic chains of destruction. 

There are two distinct stages in viscosity change with the addition of NBR in the blend. First, there is a rapid rise of viscosity with the initial addition of NBR, then beyond 50% of NBR, viscosity increases slowly, except for the preheated blends where viscosity decreases marginally at the higher level of NBR. 

Both the initial addition step and the subsequent elimination step can affect the overall rate of a nucleophilic acyl substitution reaction, but the addition step is generally the rate-limiting one. Thus, any factor that makes the carbonyl group more reactive toward nucleophiles favors the substitution process. 

When an alkene reacts with an electrophile, such as HC1, initial addition of H+ gives an intermediate cation and subsequent reaction with Cl" yields an addition product (Section 6.7). When an enol reacts with an electrophile, however, only the initial addition step is the same. Instead of reading with Cl- to give an addition product, the intermediate cation loses the -OH proton to give an cr-substituted carbonyl compound. The general mechanism is showm in Figure 22.3. 

Molozonide (Seclion 7.9) The initial addition product of ozone with an alkene. 

Methyl 3,6-di-fert-butyl-1 //-azepine-1 -carboxylate (8), on heating with one equivalent of methyl azidoformate, yields a separable mixture of 2,6-and 2,8-diazabicyclooctadienes 10 and 11.145 Initial addition of the nitrene to C4-C5 of the azepine ring, followed by a [1,3]-C or [1,3]-N shift in the resulting azahomoazepine 9, accounts for the products. 

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