Ad£3 mechanism

Electrophilic addition of HC1 to triple bonds can apparently also go by bi-or termolecular mechanisms. Thus in acetic acid 3-hexyne (14) gives predominantly anti addition through an Ad3 pathway, but 1-phenylpropyne (15), which can form the resonance-stabilized vinyl cation (16), gives predominantly syn addition through an ion pair Ad 2 mechanism.27... 

Experimental data are presented which describe the acid catalyzed dehydration chemistry of 1-propanol and 2-propanol in supercritical water at 375 C and 34.5 MPa. The data for 1-propanol dehydration are kinet-ically consistent with the acid catalyzed E2 mechanism, but not consistent with the related El mechanism. Neither the Ad 3 mechanism nor the Ad 2 mechanism is able to mimic the kinetic behavior of 2-propanol formation. The steady state idealization of the E2 mechanism does not represent the true kinetic behavior of the E2 mechanism over the range of experimental conditions presented in this paper. 

The kinetics of this reaction are second order, as would be expected for the formation of a relatively stable carbocation by an Ad -2 mechanism. ... 

Alkyl-substituted acetylenes can react with HCI by either the Ad S or the Ad 2 mechanism. The Ad S mechanism leads to anti addition. The preference for one or the other mechanism depends on the reactant structure and the reaction conditions. Added halide ion promotes the Ad S mechanism and increases the overall rate of reaction. " Reaction of 4-octyne with TFA in CH2CI2 containing O.l-l.OMBr leads mainly to Z-4-bromo-4-octene by an anti addition. The presence of Br greatly accelerates the reaction as compared to reaction with TFA alone, indicating the involvement of the Br in the rate-determining protonation step. " ... 

Ad 2 mechanism a bimolecular 1,2-addition of an electrophilic reagent to an alkene via a cationic intermediate... 

These reactions proceed via an Ad 2 mechanism involving a rate-limiting proton transfer to the jS-carbon and formation of vinyl cation 119, which reacts rapidly with H2O to give consequently enol 120, mixed anhydride 121 and the final products (equation... 

Next an alkyl halide (the alkylating agent) is added to the solution of sodium acetylide Acetylide ion acts as a nucleophile displacing halide from carbon and forming a new carbon-carbon bond Substitution occurs by an 8 2 mechanism... 

To the acid chloride, mechanically stirred and heated on the steam bath, is added 2.5 kg. (805 ml. 15.6 moles) of dry bromine as rapidly as it will react (Note 5). The addition requires about 12 hours. The contents of the flask are stirred and heated an additional 2 hours, transferred to a dropping funnel (Note 6), and added in a thin stream to 5 1. of absolute ethyl alcohol, which has previously been placed in a 12-1. flask provided with a stopper carrying an effleient reflux condenser, a separatory funnel, and a mechanical stirrer. The resulting vigorous reaction is controlled by external cooling. After the dibromoacid chloride has been added, the reaction mixture is allowed to stand at room temperature overnight and is then poured into 5 1. of cold water. The top alcoholic aqueous layer is decanted and extracted once with 8 1. of ether. The oily bottom layer is dissolved in the ether extract, washed first with 1 1. of a 2% sodium bisulfite solution, then with two 1-1. portions of 3% sodium carbonate solution, and finally with several portions of water. The ether solution is dried over 175 g. of potassium carbonate the solvent is distilled on the steam bath. The yield of residual ester (Note 7) amounts to 2260-2400 g. (91-97% of the theoretical amount). 

The crude 2-(p-nitrobenzenesulfonamido)-pyrimidine from the preceding step was suspended in 130 parts alcohol and 1.5 parts of concentrated hydrochloric acid were added. The suspension was then heated to reflux and 30 parts of iron powder were added with mechanical stirring. The mixture was refluxed and stirred for 24 hours with r"-asional addition of concentrated hydrochloric acid. The reaction mixture was then made slightly basic and filtered hot and the residues were extracted with several portions of boiling alcohol. The filtrate and wash solutions were combined and evaporated. The 2-(sulfanilamido)-pyr-imidine was recrystallized from boiling water with decolorizing charcoal added, according to U.S. Patent 2,410,793. 

Forty-three grams (0.25 mole) of />-bromoaniline (Note 1) and 20 cc. of water are warmed in a 400-cc. beaker until the bromoaniline melts, and then 50 cc. of concentrated hydrochloric acid (sp. gr. 1.19) is added with mechanical stirring. The mixture is heated and stirred until solution is practically complete (Note 2). The beaker is then set in a dish of ice water and the solution is stirred as it cools in order to precipitate the />-bromoaniline hydrochloride in fine crystals. A few small pieces of ice are added and the cold (about 0-5 °) suspension is diazotized with a solution of 18 g. of sodium nitrite in 36 cc. of water to an end point with starch-iodide paper. 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

Mechanical design of the adsorber then takes up the remainder of the engineering effort to produce a workable adsorption process design. Once a vessel is sized to provide the required inventory of adsorbenf we need to provide the mechanical details, which include flow distribution devices, bed supports and the required vessel wall thickness to withstand the working pressure and added stresses encountered during regeneration and repeated de-pressurization and re-pressurization. 

To a 100 ml three-necked flask equipped with a mechanical stirrer, condenser, and an addition funnel are added 2.0 gm (0.020 mole) of ethyl propio-late and 25 ml of absolute ethanol. The stirred solution is cooled to 0°C and then 3.0 gm (0.067 mole) of dimethylamine is slowly added. The reaction mixture is stirred for 2.5 hr at 0°C, concentrated under reduced pressure, and then distilled to afford 2.1 gm (74%), b.p. 90°-91°C (2.3 mm). 

C) Colloidal Lead Azide (abbrd as CL A) or Type II (US) is nondextrin ated LA of very small (3-4 micron) particle size, patented in 1933 by Rinkenbach (Ref 2). For its prepn, to an aq soln contg 4% of Na azide was rapidly added, while mechanically agitating and maintaining the temp at 25°, a soln of Pb nitrate or Pb acetate in slight excess of the amt necessary for the equation ... 

To a 5-1. three-necked flask, equipped with a sealed mechanical stirrer, a dropping funnel, and a take-ofl reflux condenser, are added 2 1. of sulfur-free toluene and two boiling chips. The... 

Evidence for a possibility that both the [2+2] and the [3+2] mechanism might well be involvec in the AD process was detailed by Sharpless [38]. Nonlinear Hammett plots for the AD in the presence of DHQD-CLB revealed that under the usual AD conditions a metallaoxetane pathway is favored, whereas for certain substrate ligand combinations a [3+2] mechanism is evidenced. 

Equation 2 is based on the data of Boyle and Mahlman (25, 26). These results agree with the ad hoc mechanism considered above for the effect of N08 on G(Ce+3), with the added assumption that H2 results from the... 

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