Barium hydroxide.octahydrate

A solution of dibenzo[c,g][l,2]diazocine (206 mg, 1 mmol) and barium hydroxide octahydrate (0.5 g, 1.68 mmol) inluxing EtOH (50 mL) was treated with powdered zinc (0.5 g). Afterluxing for a few minutes, the solution became colorless and heating was discontinued. Dry ice (ca. 5 g) was added in small portions and the resulting suspension was filtered. The filtrate was evaporated to 20 mL and cooled to 0 C to afford colorless crystals yield 82 ing (40%) mp 168-169 C (dec.). 

FIGURE 6.9 The endothermic reaction between ammonium thiocyanate, NH4SCN, and barium hydroxide octahydrate, Ba(0H)2-8H20, absorbs a lot of heat and can cause water vapor in the air to freeze on the outside of the beaker. 

Fluoroacetic acid.1 A few drops of phenolphthalein solution are added to a mixture of methyl fluoroacetate (46-0 g., 0-5 mol.) and water (100 c.c.) and then powdered barium hydroxide octahydrate (78-9 g., 0-25 mol.) is added in small portions, the mixture being mechanically stirred after each addition until the alkaline reaction has disappeared. The resultant liquid is then made acid, if necessary by the addition of a few drops of methyl fluoroacetate, filtered and the filtrate concentrated to about 100 c.c. on a water-bath. The liquid is cooled and methylated spirit (500 c.c.) added in order to precipitate the barium fluoroacetate, which is filtered off, drained and dried, but not recrystallized yield 69-0 g. (95-0 per cent). 

According to the Lewis theory, alkaline earth metal hydroxides are weaker bases than their oxides, the order of the strength of the basic sites being Ba(OH)2> SrO(OH)2 > Ca(OH)2 > Mg(OH)2. The hydroxides have been used recently as solid catalysts for organic transformations, such as the conjugate addition of methanol to a, S-unsaturated carbonyl compounds (12), cyanoethylation of alcohols (163,164), and transesterification reactions (166,167,171,172) which are described above. The extensive work of Sinisterra et al. (282) on the number and nature of sites and on the catalytic activity of the most basic alkali metal hydroxide, Ba(OH)2, is emphasized. It was found that commercial barium hydroxide octahydrate can be converted into... 

Stabilization of a radical anion of humic acid may be caused by an adsorption effect. Bijl (3) observed that solid barium hydroxide octahydrate turned blue when placed in a solution of quinhydrone the blue solid was highly paramagnetic. Under the conditions we used for preparing these salts, insoluble sodium humate (with a large surface area) could have stabilized the anion radical by adsorption from the basic solution. Weiss and McNeil (18) observed a similar phenomenon with base soluble xanthenes, and proposed that biradicals may be formed in such a system. His compounds, however, do not appear to have the structural requirements to satisfy such a stabilized system. The recent report by Weber (29) on the spin content increase associated with the basification of a naphthoquinone-naphthohydroquinone system seems to parallel our observations quite closely. 

To a suspension of 2 (6.0 g, 19 mmol) in boiling water (100 mL) solid barium hydroxide octahydrate (3.0 g) was slowly added while stirring. The mixture was additionally heated for 5 min and then rapidly cooled with ice to room temperature. The solution was extracted with ether, saturated with sodium chloride, then acidified to pH 6 and... 

We saw in Section 8.5 that an enthalpy change is often called a heat of reaction because it is a measure of the heat flow into or out of a system at constant pressure. If the products have more enthalpy than the reactants, then heat has flowed into the system from the surroundings and AH has a positive sign. Such reactions are said to be endothermic (endo means "within," so heat flows in). The reaction of 1 mol of barium hydroxide octahydrate with ammonium chloride, for example, absorbs 80.3 kj from the surroundings (AH° = +80.3 kj). The surroundings, having lost heat, become so cold that water freezes around the outside of the container (Figure 8.6). 

FIGURE 8.6 The reaction of barium hydroxide octahydrate with ammonium chloride is so strongly endothermic and draws so much heat from the surroundings that the temperature falls below 0°C and moisture freezes around the container. 

Barium hydroxide octahydrate, Ba(OH)2 8 H20, is a crystalline compound that contains eight water molecules clustered around the barium atom. We ll learn more about hydrates in Section 14.15. 

We ve said on several occasions that chemical and physical processes occur spontaneously only if they go "downhill" energetically so that the final state is more stable and has less energy than the initial state. In other words, energy must be released for a process to occur spontaneously. At the same time, though, we ve said that some processes occur perfectly well even though they are endothermic and absorb heat. The reaction of barium hydroxide octahydrate with ammonium chloride shown in Figure 8.6, for example, absorbs 80.3 kj of heat (AH° = +80.3 kj) and leaves the surroundings so cold that moisture freezes around the outside of the container. 

What s going on How can the spontaneous reaction of barium hydroxide octahydrate with ammonium chloride release energy yet absorb heat The answer is that, in the context of a chemical reaction, the words "energy" and "heat" don t refer to exactly the same thing. There is another factor in addition to heat that determines whether energy is released and thus determines whether a reaction takes place spontaneously. We ll take only a brief look at this additional factor right now and return for a more in-depth study in Chapter 17. 

What do a melting ice cube and the reaction of barium hydroxide octahydrate have in common The common feature of these and all other spontaneous processes that absorb heat is an increase in the amount of molecular disorder, or randomness, of the system. The eight water molecules rigidly held in the Ba(OH)2 8 H20 crystal break loose and become free to move about in the aqueous liquid product similarly, the rigidly held H20 molecules in the ice lose their crystalline ordering and move around more freely in liquid water. 

In a typical experiment, benzaldehyde (106 mg, 1 mmol) was added to the finely powdered paraformaldehyde (60 mg, 2 mmol). To this mixture, powdered barium hydroxide octahydrate (631 mg, 2 mmol) was added in a glass test tube and the reaction mixture was placed in an alumina bath (neutral alumina 125 g, mesh 150, Aldrich bath 5.7 cm diameter) inside a household microwave oven and irradiated for the specified time at its full power of 900 W intermittently or heated in an oil bath at 100-110 °C. On completion of the reaction, as indicated by TLC (hexane-EtOAc, 4 1, v/v), the reaction mixture was neutralized with dilute HC1 and the product extracted into ethyl acetate. The combined organic extracts were dried over anhydrous sodium sulfate and the solvent removed under reduced pressure. The pure benzyl alcohol (99 mg, 91%), however, is obtained by extracting the reaction mixture with ethyl acetate prior to neutralization and subsequent removal of the solvent under reduced pressure. 

Palladium on barium sulphate (5% Pd) is prepared as follows. Dissolve 4.1 g of palladium chloride (1) in 10 ml of concentrated hydrochloric acid and dilute with 25 ml of water. Add all at once 60 ml of 3 m sulphuric acid to a rapidly stirred, hot (80 °C) solution of 63.1 g of barium hydroxide octahydrate in 600ml of water contained in a 2-litre beaker. Add more 3 m sulphuric acid to render the suspension just acid to litmus. Introduce the palladium chloride solution and 4 ml of 40 per cent formaldehyde solution into the hot mechanically-stirred suspension of barium sulphate. Render the suspension slightly alkaline with 30 per cent sodium hydroxide solution, continue the stirring for 5 minutes longer and allow the catalyst to settle. Decant the clear supernatant liquid, replace it by water and resuspend the catalyst. Wash the catalyst by decantation 8-10 times and then collect it on a medium-porosity sintered glass funnel, wash it with five 25 ml portions of water and suck as dry as possible. Dry the funnel and contents at 80 °C, powder the catalyst (48 g) and store it in a tightly stoppered bottle. 

Hydrolysis to glycine. Boil a suspension of 79 g (0.25 mol) of barium hydroxide octahydrate in 175 ml of water in a 500-ml round-bottomed flask and add in portions 21 g (0.1 mol) of aminoacetonitrile sulphate. Fit a reflux condenser and continue boiling until no more ammonia is evolved (about 3 hours). Transfer the suspension to a beaker, add 50 per cent v/v aqueous sulphuric acid (about 20 ml) until precipitation of the barium is complete and the solution is slightly acidic, and digest on a steam bath. Filter the suspension through a medium-speed filter paper (e.g. Whatman No. 30) using gentle... 

The primary hydroxyl group of various 3-O-protected iV-acetyl-glucosaminides (1) has been selectively benzylated by stirring the carbohydrate with approx. 1 molar equiv. of benzyl bromide, excess barium oxide and barium hydroxide octahydrate in... 

Silver oxide in DMF was successfully applied for the regioselective reaction of (26) with allyl bromide to give compound (27) in 74% yield [231]. Hydroxyl groups in. positions 2 and 6 in cycloheptaamylose were selectively protected by reaction with allyl bromide, barium oxide, and barium hydroxide octahydrate in a DMF-DMSO mixture [232]. 

Ethyl 2-chloro-2-formylacetate Barium hydroxide octahydrate Lithium aluminum hydride 4-Nitrophenyl chloroformate Phosphorus pentasulfide Methylamine... 

A suspension of 32 g of the crude resultant compound of step 5 and 55.5 g (176 mmol) of barium hydroxide octahydrate in 400 ml of water was refluxed for 4 h. The resulting mixture was filtered, and the residue was rinsed with dioxane. The combined filtrates were concentrated to a volume of approximately 200 ml and extracted with 4 x 400 ml portions of chloroform. The combined organic layers were dried over Na2S04, filtered, and concentrated in vacuo. The residue was purified by silica gel chromatography using first 2% isopropylamine in chloroform and then 2% isopropylamine/2% methanol in chloroform to provide 10.1 g (81%) of the pure desired compound as a white solid. 

Silver oxide is prepared by pouring slowly and with stirring a hot, filtered solution of barium hydroxide octahydrate in water (1 10, w/v) into a hot solution of silver nitrate (1 5, w/v) and filtering the precipitated silver oxide. After thorough washing with hot water the product is dried in a vacuum oven at 60°C and stored in a tightly closed dark container. Freshly prepared material is recommended. 

Some types of ionic compounds can absorb water so that each formula unit is attached to a specific number of water molecules. They are called hydrates. Ba0H2 8H20 is called barium hydroxide octahydrate. CaS04 2H20 is called calcium sulfate dihydrate. Can you see the pattern Try naming MgS04 7H20. Use Table 3.8 to help you. You will learn more about hydrates in Chapter 6. 

Baryta water (saturated). Shake 5 g barium hydroxide octahydrate, Ba(0H)2.8H20, with 100 ml water. Allow to stand for 24 hours. Use the clear supernatant liquid for the tests. 

There are fire risks associated with the use of sodium hydride and alternative, innocuous bases would be welcome for large scale work One possibility is a mixture of barium oxide and barium hydroxide octahydrate in DMF. In the example shown in Scheme 4 191,355 the reaction is quite slow (7 days) and the yield only 55% but the method deserves further scrutiny. Another metal alkox-ide-based procedure for the regioselective protection of an equatorial alcohol proceeds via the stannylene derivative (see section 4,3.3)356... 

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