For example, cyclocondensation of ketals 59 affords imidazo-1,4,2-benzodithiazines 60 (Equation 8) <1997APP293>. Nitric acid accepts the proton in an acid‐base reaction. #":CN"^"-" + "CH"_3"Br" → "CH"_3"CN" + ":Br"^"-"#, An electrophilic substitution is a reaction in which an electrophile #"E"# substitutes for another atom or group #"Y"# in a compound #"R-Y"#. One important example is the replacement of the metal atom in an organometallic compound by hydrogen: The decomposition of a Grignard reagent by acid is an example. In the above reaction, a #"Br"# atom substitutes for a hydrogen atom. Semicarbazides 63 react with POCl3 to give triazolo-1,4,2-benzothiazines 64, possibly according to the mechanism depicted in Scheme 2 <2003BMC1259>. The addition of HCl to electron-deficient alkenes provided a useful approach to functionalized organic chlorides. Recent examples include the preparation of a pyrrolo[2,3-c]pyrazole 165 by acid-catalyzed condensation of 163 and 164 (Equation 37) <1999SC311> and the reaction of 3-(4-pyrazolyl)acrylic acids 166 with excess thionyl chloride in the presence of benzyltriethylammonium chloride (BTEAC) to afford 4-chlorothieno[2,3-c]pyrazole-5-carbonyl chlorides 167 (Equation 38) <2003RJO893, 2003ZOK942>. Hydrogen chloride and the other hydrogen halides add on in exactly the same way. The first step in a mechanism is reaction of the nucleophilic oxygen of the carbonyl group with the positive end of the HCl molecule. 2. However, only very active electrophiles are suitable, for example, benzenesulfonyl azide which on reflux in acetonitrile with 258 yields 259 (Equation 70) <1998RJC530>. At higher temperatures, alkene elimination occurs. described an efficient procedure for the synthesis of homoallylic halides. Electrophilic addition using Cl2, I2, and CF3CO2H gives the analogous clusters [Ru3(μ-H)2(CO)6(PPh3)3(μ3-η2-EtC2Et)(μ2-X)]+ (X=Cl 80, I 81, H). Addition of chlorine to spirophosphenium cation 262 generates the six-coordinate 263, which can be converted to the more stable tetrachlorocatechol derivative 264 by addition of bis(trimethylsiloxy)tetrachlorobenzene (Scheme 36) <1998RJC530>. Treatment of the anti-apicophilic spirophosphorane 266 with a phenyl group at the α-position under the same conditions generates a stable six-coordinate tricyclic spirophosphoranide 95 (Equation 72) <2002JA13154>. The combination of other HCl precursors such as SOCl2 or (COCl)2 with silica gel or alumina could give higher yields (equations 8 and 9). Williams, in Comprehensive Heterocyclic Chemistry III, 2008. Similarly, 3,3-dimethyl-1-butene afforded a mixture of the unrearranged and rearranged chlorides; the selectivity is affected by the nature of substrate and the reaction conditions (equation 11). Eric Block, Adrian L. Schwan, in Comprehensive Organic Synthesis, 1991. Our sole focus is these products and the customers that use them. For example, hydrogen chloride adds to ethene to make chloroethane: The only difference is in how fast the reactions happen with the different hydrogen halides. Gregory Roos, Cathryn Roos, in Organic Chemistry Concepts, 2015. The mechanisms are different for aliphatic and aromatic nucleophilic substitutions, but the overall result is the same: A nucleophile #"Y"# replaces a leaving group #"X"#. The bromide ion also reacts at the primary carbon atom (resonance form II) to give the 1,4-addition product. In electrophilic addition to carbon-carbon double bonds, a positive species approaches in the first step converting the pair of π-electrons into an s-pair. In the above reaction, a #"Br"# atom substitutes for a hydrogen atom. Thus, surface-mediated addition is believed to proceed via a stepwise process involving the carbocation intermediate. Electrophilic addition at N(2) in 3-substituted-1,4,2-benzodithiazines leads to intramolecular cyclization. What conditions favour nucleophilic substitution? The protonation at the C-2 position leads to a more stable cyclopropylcarbinyl cation. This is a 1,2-addition reaction. W. Li, J. Zhang, in Comprehensive Organic Synthesis II (Second Edition), 2014. The key difference between nucleophilic and electrophilic addition is that, in nucleophilic addition reactions, an electron-rich component combines with a molecule whereas, in electrophilic addition reactions, either an electron-deficient species or a neutral compound with empty orbitals combines with a molecule. See all questions in SN1 and SN2 Reactions. Electrophilic aliphatic substitutions are relatively uncommon. For example, the reaction of (R)-limonene with 0.5 equivalent of SOCl2 at room temperature in the heterogeneous media SiO2/CH2Cl2 produced (R)-α-terpinyl chloride in good yield with a little racemization (equation 14),21 whereas the traditional homogeneous conditions require a slow addition of dry gaseous HCl to dry limonene at low temperature and long reaction time.22 Under similar reaction conditions, isoprene undergoes 1,4-addition to afford prenyl chloride in 82% yield (equation 15).23. The resulting cation is a resonance hybrid with a partial positive charge on carbon as well as on oxygen: The electrophilic β position now reacts with the nucleophilic chloride ion to give an enol, which then tautomerizes to the keto form.


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