Sodium hydroxide proton transfer

Dissociation extraction is the process of using chemical reac tion to force a solute to transfer from one liquid phase to another. One example is the use of a sodium hydroxide solution to extract phenolics, acids, or mercaptans from a hydrocarbon stream. The opposite transfer can be forced by adding an acid to a sodium phenate stream to spring the phenolic back to a free phenol that can be extrac ted into an organic solvent. Similarly, primary, secondary, and tertiary amines can be protonated with a strong acid to transfer the amine into a water solution, for example, as an amine hydrochloride salt. Conversely, a strong base can be added to convert the amine salt back to free base, which can be extracted into a solvent. This procedure is quite common in pharmaceutical production. 

The kinetics of proton transfer from the C-2a position of 2-(l-methoxybenzyl)thiazolium salts was studied for the p-H and /)-NMeJ derivatives by H NMR spectroscopy. The study was carried out by mixing the salts rapidly with sodium hydroxide in a stopped-flow instmment and monitoring the progress of enamine formation and decomposition in the visible region of the spectmm. Under these conditions the thiazolium ring opened, the H NMR spectrum of the product being consistent with both as- and /ra r-stereochemistry about the newly formed enamine bond (Scheme 23) <1997JA2356>. 

Reaction of l-chloro-l,3,3-triphenylallene (19) with p-toluidine in the presence of silver triflate gave 2,3,4-triphenylbuta- l-aza-1,3-diene derivative 22a via a novel l, 2-phenyl shift not reported earlier in the solvolysis of allenyl chlorides. The reaction takes place via the formation of the allenyl cation, which is captured as its canonical propargyl cation, first affording the protonated amine 20 (R = Me). Proton transfer from the nitrogen to the acetylenic carbon is followed by migration of a phenyl group in the intermediate vinyl cation 21 (R = Me) to afford the iminium triflate 22a. The latter is hydrolyzed by aqueous sodium hydroxide to the azabutadiene 23 (equation 5). Similar reaction of 19 with aniline and silver triflate afforded the corresponding iminium triflate 22b. ... 

Draw a reasonable proton transfer mechanism for the following reaction catalyzed by sodium hydroxide in heavy water. D stands for deuterium. Treat D2O just like H2O. 

The donor-acceptor principle is an important basic concept in modern chemical education acid-base reactions, redox reactions and complex reactions explain a huge number of chemical changes. One important group of donor-acceptor reactions are the acid-base reactions protons (H+ ions) transfer from one species to another species. One example, in the neutralization of sulfuric acid with sodium hydroxide a proton is moving from one hydronium ion H30 + (aq) of the acid solution to one hydroxide ion OH (aq) ion of the hydroxide solution. Broensted s key concept will be considered in this chapter. 

When sodium hydroxide solution is added, the H3O ion transfers a proton to the OH ion of the base (with the product water shown here as HOH) ... 

Many of the reactions catalysed involve the transfer of protons to and from the zeolite (Figure 2.8). As this is the characteristic function of an acid, the H-forms of the zeolite (those in which the adsorbed ions are H+) are sometimes referred to as solid acid catalysts. Synthetic zeolites are often prepared in concentrated solutions of sodium hydroxide, which leaves Na" as the counter ion in the zeolite pores, the Na-zeolite. The usual way to prepare H-zeolites is to exchange these metal ions for ammonium ions (NH4" ), and then heat the ammonium form of the zeolite to about 500 °C. Ammonia (NH3) is then driven off, leaving H+ ions to balance the negative charges on the silicate structure. This is the reverse of the reaction shown in Figure 2.8, when the base B is NH3. 

The last step in the base hydrolysis of an ester is proton transfer from the carboxylic acid molecule to the alkoxide ion. This reaction is virtually irreversible. From a practical standpoint, base hydrolysis is a more useful process as, with for example sodium hydroxide, the acid is now in its salt form. This means that the products can be separated much more easily. 

Sodium hydroxide has been the most commonly used base in experimental nitroalkane proton transfer reaction studies.However, the computational studies of these reactions have generaUy been with hydroxide ion without the sodium counter ion. Recently a computational study of the proton transfer reactions of the three simple nitroalkanes in the presence of NaOH in water has been carried out and it was found that the presence of Na had an enormous effect on the energetics of the reactions. Double potential energy well diagrams, much like those found for the Sn2 reactions, were recorded for the proton transfer reactions of NM, NE and 2-NP with hydroxide ion in water. The computations included two explicit water molecules in the water cavity. The Gibbs free energies and enthalpies observed for the reactant complex (CPI), the TS and the product complex (CP2) both in the presence and absence of sodium ion and two explicit water molecules are summarized in Table 1.24. 

Write the molecular equation and then the net ionic equation for the neutralization of nitrous acid, HNO2, by sodium hydroxide, NaOH, both in aqueous solution. Use an arrow with H over it to show the proton transfer. 

Equivalent weights of acids and bases. One equivalent of an acid is the quantity that transfers (gives up) 1 mole ofH (1 mole of protons). Correspondingly, 1 eq of a base is the quantity that accepts 1 mole of H. Sodium hydroxide, NaOH, can react with phosphoric acid, H3PO4, for example, in any one of three ways ... 

Cyclic ethers can be prepared by the intramolecular Sj j2 reaction of a halogen-substituted alcohol such as a bromo alcohol. Proton transfer to a base such as sodium hydroxide gives a bromo alkoxide. If the solution is dilute, the alkoxide acts as a nucleophile, and an intramolecular reaction displaces a bromide ion. This process is shown below for 5-bromo-l-penten-l-ol. 

Miller s group reported the use of sodium salts, such as sodium arsenate (Gxmter et al., 1995), silica-supported sodium nitrates (Wadley et al., 1997), and a screening of different pore glass-supported alkali hydroxides (Tam et al., 1998). By the use of the Cs, a 49% PD yield was achieved at 280°C, while only 15% was obtained by Tam at 320°C (Tam et al., 1998). Accordingly, FT-IR studies indicated that the formation of alkali lactates via a proton transfer to the counter anion (eg, with the release of HNO3 for nitrates) was the dominant mechanism (Tam et al., 1997). For the supported NasPO/ catalyst, Na9HP04 and sodium lactate were formed (Wadley etal., 1997). 

Polymeric amines can be proton acceptors, acyl transfer agents, or ligands for metal ions. The 2- and 4-isomers of poly(vinylpyridine) (11) and (12) and the weakly basic ion exchange resins, p-dimethylaminomethylated PS (2) and poly(2-dimethylaminoethyl acrylate), are commercial. The ion exchange resins are catalysts for aldol condensations, Knoevenagel condensations, Perkin reactions, cyanohydrin formation and redistributions of chlorosilanes. " The poly(vinylpyridine)s have been used in stoichiometric amounts for preparation of esters from acid chlorides and alcohols, and for preparation of trimethylsilyl ethers and trimethylsilylamines from chlorotrimethylsilane and alcohols or amines. Polymer-suppored DBU (l,8-diazabicyclo[5.4.0]undec-7-ene) (52) in stoichiometric amounts promotes dehydrohalogenation of alkyl bromides and esterification of carboxylic acids with alkyl halides. The protonated tertiary amine resins are converted to free base form by treatment with aqueous sodium hydroxide. 

The hydroxide ion is usually not sufficiently nucleophilic to reinitiate polymerization and the kinetic chain is broken. Water has an especially negative effect on polymerization, since it is an active chain-transfer agent. For example, C s is approximately 10 in the polymerization of styrene at 25°C with sodium naphthalene [Szwarc, 1960], and the presence of even small concentrations of water can greatly limit the polymer molecular weight and polymerization rate. The adventitious presence of other proton donors may not be as much of a problem. Ethanol has a transfer constant of about 10-3. Its presence in small amounts would not prevent the formation of high polymer because transfer would be slow, although the polymer would not be living. 

Lithium hydride and sodium hydride are the only alkali metal hydrides of much practical importance. They are useful when it is desirable for proton (or hydrogen atom) transfers to accompany electron-transfer events. Because these hydrides react quickly with water to form alkali metal hydroxides and hydrogen gas, they are frequently used as drying agents, particularly for hydrocarbons and ethers. Care should be exercised in using them to dry solvents that are not predried, and they should not be used to dry alcohols or halogenated solvents. 

If ion symbols in the reacting solutions have been successfully drawn (see Fig. 7.10) and neutralization reaction is then discussed based on these drawings, one automatically comes to the correct interpretation that those hydronium ions, through the transfer of protons to hydroxide ions, react with each other to form water molecules. During the reactions, the hydrated sodium ions Na + (aq) and hydrated chloride ions Cl (aq) are not involved (see Fig. 7.14). These ions are known as spectator ions they exist as spectators ... 

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