Stirred two-phase system

The a-bromoamide (3 mmol), the amine (or its salt) (3.5 mmol) and TBA-Br (97 mg, 0.3 mmol) are added to a stirred two-phase system of aqueous NaOH (50%, 10 ml) and CHjClj (12 ml). Stirring is continued for a further 4-10 h (see Table 5.3). H20 (10 ml) is then added and the organic phase is separated and washed with H20 (3 x 50 ml) and HC1 (1M, 3 x 30 ml). The combined aqueous phases are neutralized with NaHC03 and extracted with CH2C12 (3 x 50 ml). The dried (MgS04) organic extracts are evaporated to yield the aminocarboxamide, which is purified by chromatography from silica. 

Method A The haloalkane (0.06 mol) in PhH (10 ml) is added dropwise over a period of ca. 1.5 h to the amide (0.05 mol) and TBA-HS04 (1.7 g, 5 mmol) in a stirred two-phase system of aqueous NaOH (50%, 50 ml) and PhH (50 ml) under reflux. Stirring is continued for a further 2.5 h under reflux and the mixture is then cooled to room temperature and H20 (30 ml) is added. The organic phase is separated, washed with H20 until neutral, dried (MgS04), and evaporated under reduced pressure to yield the alkylated amide. 

Cognate preparation. Ethyl (E)-but-2-enoate255 (PTC procedure). A solution of triethyl phosphonoacetate (35 mmol) and acetaldehyde (35 mmol) in dichloromethane (5 ml) is added dropwise to a stirred two-phase system consisting of dichloromethane (35 ml), aqueous sodium hydroxide (20 ml, 50%) and tetrabutylammonium iodide (0.7 g) (1). The strongly exothermic reaction is complete in 15 minutes. The organic layer is separated, washed with water (5 ml), and dried with magnesium sulphate. Evaporation of the solvent and distillation of the residue affords the product, b.p. 51-52 °C/25mmHg, in 54 per cent yield. 

It is frequently observed that in the replacement reactions discussed above significant amounts of biphenyl derivatives are present in the reaction product. Compounds of this type may be prepared deliberately by adding the aqueous diazonium salt solution to a liquid aromatic compound and then basifying the vigorously stirred two-phase system by adding sodium hydroxide (or sodium acetate) solution. 

In surfactant-based reaction media mass transfer limitations on the reaction rate are much suppressed in comparison to stirred two-phase systems without surfactants. The reason for this pronounced difference is the different characteristic length scales of the systems. This may be illustrated by the following example. Twenty grams per litre of a... 

A typical example for a stirred two-phase system with a volume fraction of 30 vol.% organic phase dispersed in water, an interfacial tension of 25 mN m-1 and a specific power input of 0.5 W L 1 shows a droplet diameter in the range of 250 pun and a specific interface of about 10 m2 L 1. These dimensions maybe estimated from simple empirical correlations between the Sauter mean diameter of the dispersed phase (zf2.3) and the characteristic Weber number (We). In case of turbulent mixing the following correlation is proposed in the literature for calculation of the mean diameter of dispersed droplets [24]... 

Cyclopentadiene can be deprotonated by dimethylamine in the presence of anhydrous TiCl, FeCl, or NiCl, to yield Cp,TiCl, (p. 290), Cp,Fe (ferrocene) or Cp,Ni (nickelocene) respectively. Ferrocene has even been prepared in a rapidly stirred two phase system (benzene/water) from FeCl, 4H,0, cyclopentadiene and potassium hydroxide using a crown ether, 18-crown-6, as a phase-transfer catalyst. 

Such a reaction is controlled by the rate of addition of the acid. The two-phase system is stirred throughout the reaction the heavy product layer is separated and washed thoroughly with water and alkaU before distillation (Fig. 3). The alkaU treatment is particularly important and serves not just to remove residual acidity but, more importantiy, to remove chemically any addition compounds that may have formed. The washwater must be maintained alkaline during this procedure. With the introduction of more than one bromine atom, this alkaU wash becomes more critical as there is a greater tendency for addition by-products to form in such reactions. Distillation of material containing residual addition compounds is ha2ardous, because traces of acid become self-catalytic, causing decomposition of the stiU contents and much acid gas evolution. Bromination of alkylthiophenes follows a similar pattern. 

The terminal R groups can be aromatic or aliphatic. Typically, they are derivatives of monohydric phenoHc compounds including phenol and alkylated phenols, eg, /-butylphenol. In iaterfacial polymerization, bisphenol A and a monofunctional terminator are dissolved in aqueous caustic. Methylene chloride containing a phase-transfer catalyst is added. The two-phase system is stirred and phosgene is added. The bisphenol A salt reacts with the phosgene at the interface of the two solutions and the polymer "grows" into the methylene chloride. The sodium chloride by-product enters the aqueous phase. Chain length is controlled by the amount of monohydric terminator. The methylene chloride—polymer solution is separated from the aqueous brine-laden by-products. The facile separation of a pure polymer solution is the key to the interfacial process. The methylene chloride solvent is removed, and the polymer is isolated in the form of pellets, powder, or slurries. 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Preparation of 2-Bromo-3-Hexyne A solution of 13B g of 3-hexyne-2-ol and 9 g of pyridine in 13B ml of anhydrous ether was treated with 175 g of phosphorus tribromide, added dropwise over a period of about 20 minutes at a temperature of about -10°C. The reaction mixture was permitted to come to room temperature while stirring for about 3 hours, and was then heated to refluxing for about 1 hour. After cooling, the reaction mixture was poured over about 50 g of crushed ice. A two-phase system formed, and the ether layer was separated, washed with dilute sodium bicarbonate solution, dried over anhydrous potassium carbonate and fractionally distilled. The 2-bromo-3-hexyne formed in the reaction was collected at 75°C at the pressure of 50 mm of mercury. 

An important aspect of nitrating toluene to nitrotoluene is the very low solubility of toluene and nitroioluenes in nitrating mix Is. Therefore the nitration proceeds in a two-phase system and the rate of nitration depends greatly on dispersion, which in turn depends on keeping the two phases efficiently stirred. This is emphasized in Fig 4, which gives the yield of MNT for a 11/64/25% nitric acid/sulfuric acid/water MA and a nitration time of 30 minutes as a function of stirring speed... 

In addition, PhCH2SCH2Ph forms 1 1 adducts with Hg2(N03)2 and 1 2 adducts with Hg 2(0104)2. Two-phase systems can be used to isolate these complexes. The Hgd) salt is dissolved in H2O or MeOH, the organic sulfur ligand is dissolved in benzene or CH2CI2 and the two solutions are stirred together. 

In practice, promising results have been obtained for several systems. For example, fair to good yields of epoxides are obtained when a two-phase system consisting of alkene and ethyl chloroformate is stirred with a buffered basic solution of hydrogen peroxide. The active oxidant is presumed to be O-ethyl peroxycarbonic acid.85... 

Method D The alcohol (11.5 mol) is added to TBA-Br (0.32 g, 1 mmol) in aqueous NaOH (50%, 5 ml) and the mixture is stirred for 5 min. A suspension of the halonitro-benzamide (0.1 mol) in PhMe (150 ml) is then added and the two-phase system is stirred at 40 C until the reaction is shown to be complete by TLC analysis. The mixture is cooled to room temperature and the organic phase is separated and evaporated. H20 (300 ml) is added and the ether comes out of solution. (Method D fails with phenols and with secondary and tertiary alcohols.)... 

Method E The halonitrophenyl sulphone (40 mmol) and TBA-Br (0.16 g, 0.5 mmol) in CH2C1, (100 ml) are added to a stirred solution of the phenol (20 mmol) in aqueous NaOH (40%, 100 ml) at room temperature. The two-phase system is stirred until the... 

Aliquat (0.2 g, 0.5 mmol) is added to the amine (l 4.5 mmol) in H20 (25 ml) and 1,2,3,4-tetrachloro-5,6-dinitrobenzene (2.0 g, 6.5 mmol) in PhMe (25 ml). The two-phase system is stirred under reflux for ca. 1 h and then cooled. The organic phase is separated, dried (MgS04), and evaporated. Chromatography of the residue from silica gives the aniline. 

The carbamoyl fluoride (8.47 mmol) in PhMe (5 ml) is added to the alcohol (8.47 mmol), NaOH (0.51 g, 12.71 mmol) and TB A-HS04 or THA-Cl (0.85 mmol) in PhMe (5 ml) and H20 (10 ml). The two-phase system is stirred until the reaction is complete, as shown by GLC analysis. The mixture is poured into PhMe (10 ml) and H20 (10 ml) and the organic phase is separated, washed well with H20, dried (Na2S04), and evaporated to yield the carbamate. 

The arene sulphonyl chloride (0.11 mol) in PhH (50 ml) is added dropwise at 20°C to a two-phase system of the alcohol (or phenol) (0.1 mol) and TEBA-Cl (0.91 g, 4 mmol) in PhH (100 ml) and aqueous NaOH (30%, 50 ml). The mixture is stirred at 20°C for 5-8 h, and the organic phase is then separated, washed well with HzO until the washings are neutral, dried (Na2S04), and fractionally distilled to yield the sulphonic ester. 

The unsaturated aldehyde (0.1 mol) is added to a two-phase system of thiolacetic acid (7.6, 0.1 mol) in aqueous NaOH (50%, 16 ml) and TBA-I (0.1 g, 0.27 mmol) in CH2CI2 (100 ml) over a period of ca. 30 min at 0°C. The mixture is stirred for 2.5 h at 0°C and then heated under reflux for 20 min. The organic phase is separated, diluted with Et20 (50 ml), washed with H20 (3 x 25 ml), and dried (MgS04). Evaporation of the solvent gives i-formyl-5-thiacyclohex-l-ene (41%) from acrolein and 1-formyl-4,6-dimethyl-5-thiacyclo-hex-l-ene (81%) from crotonaldehyde. 

The bis-sulphonamide (0.02 mol) and the a,o-dibromo compound (0.02 mol) in PhH (or PhMe) (600 ml) are added to a refluxing two-phase system of aqueous NaOH (7.5%, 100 ml) and PhH (or PhMe) (100 ml) containing TBA-I (1.85 g, 5 mmol). The mixture is stirred under reflux for 8-10 h and then cooled to room temperature. The organic phase is separated, dried (MgS04), and evaporated to yield the A-tosyl azacrown ether which, upon treatment with acid, is converted into the azacrown ether. 

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