In the presence of an excess

Iodine monochloride, formed when iodine reacts with the iodate(V) ion in the presence of an excess of concentrated hydrochloric acid. 

Kinetic measurements were performed employii UV-vis spectroscopy (Perkin Elmer "K2, X5 or 12 spectrophotometer) using quartz cuvettes of 1 cm pathlength at 25 0.1 C. Second-order rate constants of the reaction of methyl vinyl ketone (4.8) with cyclopentadiene (4.6) were determined from the pseudo-first-order rate constants obtained by followirg the absorption of 4.6 at 253-260 nm in the presence of an excess of 4.8. Typical concentrations were [4.8] = 18 mM and [4.6] = 0.1 mM. In order to ensure rapid dissolution of 4.6, this compound was added from a stock solution of 5.0 )j1 in 2.00 g of 1-propanol. In order to prevent evaporation of the extremely volatile 4.6, the cuvettes were filled almost completely and sealed carefully. The water used for the experiments with MeReOj was degassed by purging with argon for 0.5 hours prior to the measurements. All rate constants were reproducible to within 3%. 

The kinetics of nitration of benzene in solutions at c. 20 °C in carbon tetrachloride have been investigated. In the presence of an excess of benzene (c. 2-4 mol 1 ) the rate was kinetically of the first order in the concentration of benzoyl nitrate. The rate of reaction was depressed by the addition of benzoic anhydride, provided that some benzoic acid was present. This result suggested that benzoyl nitrate itself was not responsible for the nitration, but generated dinitrogen pentoxide... 

Under natural conditions various strains of Penicillium fungi produce either penicillin G or free 6-aminopenicillanic add ( = 6-APA). The techniques used to prepare analogues such as the ones given above have been (i) fermentation in the presence of an excess of appropriate adds which may be incorporated as side-chain (ii) chemical acylation of 6-APA with activated acid derivatives. 

Acetoxylchlorination of norbornene (138) proceeds with skeletal rearrangement in the presence of an excess of CuCl2 to give e.Yo-2-chloro-iyn-7-acetoxy-norbornane (139). This is a good synthetic method for ivn-7-norbornenol[163]. 

The Pd-catalyzed coupling of an acyl chloride with benzyl chloride to form the benzyl ketone 854 proceeds in the presence of an excess of Zn. In this reaction, benzyl chloride reacts with Zn to form benzylzinc, which undergoes transmetallation with acylpaliadium complex[729]. The reaction has been applied to the synthesis of riccardin B (855)[730]. 

In the presence of many metal ions, diorthohydroxyazo dyes exhibit two polarographic reduction waves, the first due to free dye and the second to metal-dye complex. Highly sensitive analytical methods based on this principle have been developed for example, Ni or Fe may be determined in the presence of an excess of aluminum thank to thiazolylazo derivatives (563). 

A voltammogram for the two-electron reduction of M has a half-wave potential of —0.226 V versus the SCE. In the presence of an excess of the ligand L, the following half-wave potentials are recorded... 

Silver(II) Compounds. Sdver(II) is stabilized by coordination with nitrogen heterocychc bases, such as pyridine and dipyridyl. These cationic complexes are prepared by the peroxysulfate oxidation of silver(I) solutions in the presence of an excess of the ligand. An extensive review of the higher oxidation states of silver has beenpubhshed (21). 

The alkyl lithium method gives high yields of -olefins from 17-ketones via the tosylhydrazones. A -Olefins are formed from 6- and 7-ketones. (Compare with the Bamford-Stevens reaction which gives A - and A -olefins, respectively.) In the presence of an excess of alkyl lithium, alkylation may occur. 

Naphthalene-1,8-dicarboxylic add, its nitro-substituted derivatives, and naphthalene-1,4,5,8 tetracarboxylic acid, on treatment with sulfur tetrafluoride at 0 C, undergo dehydration to form quantitatively the corresponding anhydrides [218, 221] Unsubstituted and mononitrated monoanhydndes react further at 200-250 °C to give derivatives of 1,1,3,3-tetrafluoro-l// naphtho[I,8 c,d]pyran Dinitronaphthalene-l,8-di-carboxyhc acid anhydndes and naphthalene 1,4,5,8 tetracarboxylic acid dianhydnde give the respective tetra- and octafluoroethers only in the presence of an excess of anhydrous hydrogen fluoride [221] (equabons 113 and 114)... 

The use of liquid NH3 to prepare compounds of elements in unusual (low) oxidation states is exemplified by the successive reduction of K2[Ni(CN)4] with Na/Hg in the presence of an excess of CN the dark-red dimeric Ni complex K4[Ni2(CN)6] is first formed and this can be further reduced to the yellow Ni° complex K4[Ni(CN)4]. The corresponding complexes [Pd(CN)4]" and [Pt(CN)4]" can be prepared similarly, though there is no evidence in these latter systems for the formation of the M dimer. A ditertiaiyphosphine complex of Pd° has also been prepared ... 

The last two of these reactions also feature a reduction in oxidation state. A closely related route is halogen exchange usually in the presence of an excess of the halogenating reagent , e.g. ... 

Thus in the presence of an excess of NH4+, which suppresses this forward reaction, and counteranions such as NOa" and C104, which have little tendency to coordinate, complexes such as [Hg(NH3)4] +, [Hg(L-L)2] + and even [Hg(L-L)3] + (L-L = en, bipy, phen) can be prepared. But, in the absence of such precautions, amino, or imino-compounds are likely to be formed, often together. Because of this variety of simultaneous reactions and their dependence on the precise conditions, many reactions between Hg and amines, although first performed by alchemists in the Middle Ages, remained obscure until the application of X-ray crystallography and, still more recently, spectroscopic techniques such as nmr, infrared and Raman. 

A spectacular application of the acyloin ester condensation was the preparation of catenaries like 11. These were prepared by a statistical synthesis which means that an acyloin reaction of the diester 10 has been carried out in the presence of an excess of a large ring compound such as 9, with the hope that some diester molecules would be threaded through a ring, and would then undergo ring closure to give the catena compound ... 

The electron affinity of radicals is considerably greater than the electron affinity of monomers, hence in the presence of monomer" ions, or in the presence of an excess of the primary electron donors, the dimeric radical ions are rapidly converted into dimeric diions,... 

Recently, Lin17 270 271 found a 3rd-order for the reaction of sucdnic and adipic adds with 1 -ethanediol in the presence of an excess of a diol. Surprisingly, he found orders 1 with respect to add and 2 with respect to alcohol. This was explained by the fact that acid... 

Such reactions may be the reason why Fradet and Marechal230 observed a poor catalytic activity when performing model studies in the presence of an excess of acid. 

When the reaction is carried out in the presence of an excess of add, a strong decrease in the reaction rate occurs at high conversion. In contrast, the catalyst is stabilized when an excess of alcohol is present. 

Trimethylsilyl halides can also be used for analogous reactions with arenediazo-nium tetrafluoroborates, as shown by Keumi et al. (1989). These authors treated 2-fluorenediazonium tetrafluoroborate in A/,Af-dimethylformamide or -acetamide with trimethylsilylchloride, -bromide, or -iodide in the presence of an excess of N-chlorosuccinimide, Af-bromosuccinimide, or methyl iodide, respectively, at 60 °C (Cl, Br) or at room temperature (I). The yields of the 2-halofluorenes were good in addition fluorene, the product of hydro-de-diazoniation, was obtained, if the reaction was run in tetrahydrofuran/Af,7V-dimethylformamide mixtures. The mechanism of these reactions, as well as that of the corresponding azido-de-diazoniation, is uncertain (see also Secs. 10.2 and 10.7). 

Hydroxyalkyl sulphoxides 515 can be dehydrated either by treatment with phosphoric acid (equation 315) or by the alkylation with Mel in the presence of an excess of sodium hydride611 (equation 316). For other dehydration reactions see References 475 and 505 (Section IV.A.2.d). For elimination of amines see References 164 and 529 (Section IV.A.2.e). 

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