Preparation Laboratory

There are today two methods of interest, (a) the laboratory preparation, and (b) commereial preparation. 

Before commencing any experimental work, the relevant up-to-date MSDSs must be studied and the appropriate safety requirements observed. There are often local or in-house regulations for handling certain materials such as MOCA. These must be strictly observed. All people near any isocyanate must take special care not to inhale any traces of its vapor, as these may cause respiratory problems. 

If available, the analysis of the raw materials should be studied, especially with regard to purity, potential interfering contaminants, functionality, moisture, and acidity/alkalinity. The molecular weight is often not given directly but must be calculated from the OH value and the functionality of the polyol (see Appendix 5 for formula). 

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Describe the laboratory preparation, from aluminium, of (a) anhydrous aluminium chloride, (b) potassium aluminium sulphate dodecahydrate. 

Outline the laboratory preparation of a sample of dinitrogen tetroxide. Describe and explain what happens when it is heated from 290 K to 900 K. Suggest electronic structures for dinitrogen tetroxide and the other nitrogen-containing molecules formed from it on heating to 900 K. Point out any unusual structural features. 

IV) oxide, the latter being used in the eommon laboratory preparation of oxygen from hydrogen peroxide (p. 260. ... 

Note on the laboratory preparation of monoethylaniline. Although the laboratory preparation of monomethyl- or monoethyl-aniline is hardly worth whUe, the following experimental details may be useful to those who wish to prepare pure monoethylaniline directly from amline. In a flask, fitted with a double surface reflux condenser, place 50 g. (49 ml.) of aniline and 65 g. of ethyl bromide, and boU gently for 2 hours or until the mixture has almost entirely sohdified. Dissolve it in water and boil off the small quantity of unreacted ethyl bromide. Render the mixture alkaUne with concentrated sodium hydroxide solution, extract the precipitated bases with three 50 ml. portions of ether, and distil off the ether. The residual oil contains anihne, mono- and di-ethylaniline. Dissolve it in excess of dilute hydrochloric acid (say, 100 ml. of concentrated acid and 400 ml. of water), cool in ice, and add with stirring a solution of 37 g. of sodium nitrite in 100 ml. of water do not allow the temperature to rise above 10°. Tnis leads to the formation of a solution of phenyl diazonium chloride, of N-nitrosoethylaniline and of p-nitrosodiethylaniline. The nitrosoethylaniline separates as a dark coloured oil. Extract the oil with ether, distil off the ether, and reduce the nitrosoamine with tin and hydrochloric acid (see above). The yield of ethylaniline is 20 g. 

Among compounds other than simple alkyl halides a halo ketones and a halo esters have been employed as substrates m the Gabriel synthesis Alkyl p toluenesul fonate esters have also been used Because phthalimide can undergo only a single alkyl ation the formation of secondary and tertiary amines does not occur and the Gabriel synthesis is a valuable procedure for the laboratory preparation of primary amines... 

Intermediate formation of formyl chloride is not necessary since the actual alkylating agent, HCO", can be produced by protonation of carbon monoxide or its complexes. However, it is difficult to obtain an equimolar mixture of anhydrous hydrogen chloride and carbon monoxide. Suitable laboratory preparations involve the reaction of chlorosulfonic acid with formic acid or the reaction of ben2oyl chloride with formic acid ... 

Oligomers of phosgene, such as diphosgene [503-38-8] (COCl2)2, have found use in the laboratory preparation of isocyanates. Carbamoyl chlorides, A[,A/-disubstituted ureas, dimethyl- and diphenylcarbonates, and arylsulfonyl isocyanates have also been used to convert amines into urea intermediates, which are subsequendy pyroly2ed to yield isocyanates. These methods have found appHcations for preparation of low boiling point aUphatic isocyanates (2,9,17). 

Ketones are an important class of industrial chemicals that have found widespread use as solvents and chemical intermediates. Acetone (qv) is the simplest and most important ketone and finds ubiquitous use as a solvent. Higher members of the aUphatic methyl ketone series (eg, methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone) are also industrially significant solvents. Cyclohexanone is the most important cycHc ketone and is primarily used in the manufacture of y-caprolactam for nylon-6 (see Cyclohexanoland cyclohexanone). Other ketones find appHcation in fields as diverse as fragrance formulation and metals extraction. Although the industrially important ketones are reviewed herein, the laboratory preparation of ketones is covered elsewhere (1). 

Nitric acid is a strong monobasic acid, a powerful oxidising agent, and nitrates many organic compounds. Until the end of the nineteenth century, it was made by heating a metallic nitrate salt with less volatile concentrated sulfuric acid. Removal of the volatile nitric acid permits the reaction to go to completion. This method is still used for laboratory preparation of the acid. 

Synthesis by oxidation remains the first choice for commercial and laboratory preparation of quinones the starting material (1) provided the generic name quinone. This simple, descriptive nomenclature has been abandoned by Chemicaly hstracts, but remains widely used (2). The systematic name for (2) is 2,5-cyclohexadiene-l,4-dione. Several examples of quinone synonyms are given in Table 1. Common names are used in this article. 1,2-Benzoquinone (3,5-cydohexadiene-l,2-dione) (3) is also prepared by oxidation, often with freshly prepared silver oxide (3). Compounds related to (3) must be prepared using mild conditions because of their great sensitivity to both electrophiles and nucleophiles (4,5). 

Thiosulfuric Acid. Thiosulfuiic acid [14921 -76-7] is relatively unstable and thus cannot be recovered from aqueous solutions. In laboratory preparation, a lead thiosulfate [26265-65-6] solution is treated with H2S to precipitate PbS, or a concentrated solution of sodium thiosulfate [7772-98-7] is treated with HCl and cooled to — 10°C to crystalline NaCl. Aqueous solutions of thiosulfuric acid spontaneously decompose to yield sulfur, SO2, and polythionic acids, H2S O. Thiosulfuric acid is a strong acid comparable to sulfuric acid. Dissociation constants, = 0.25, = 0.018, have been... 

Most of the methods for preparing BBr are similar to those for preparation of BCl. A convenient laboratory preparation involves reaction of AIBr. and BF or BF (2). A procedure for the preparation of labeled BBr from the reaction of BF and AIBr. has also been described (69). 

Boron Triiodide. Boron ttiiodide is not manufactured on a large scale. Small-scale production of BI from boron and iodine is possible in the temperature range 700—900°C (70—72). Excess I2 can be removed as Snl by reaction with Sn, followed by distillation (71). The reaction of metal tetrahydroborates and I2 is convenient for laboratory preparation of BI (73,74). BI can also by synthesized from B2H and HI in a furnace at 250°C (75), or by the reaction of B with excess Agl or Cul between 450—700°C, under vacuum (76). High purity BI has been prepared by the reaction of I2 with mixtures of boron carbide and calcium carbide at elevated temperatures. 

Commercial manufacture of methyl bromide is generally based on the reaction of hydrogen bromide with methanol. For laboratory preparation, the addition of sulfuric acid to sodium bromide and methanol has been used (80). Another method involves the treatment of bromine with a reducing agent, such as phosphoms or sulfur dioxide, to generate hydrogen bromide (81). 

In laboratory preparations, sulfuric acid and hydrochloric acid have classically been used as esterification catalysts. However, formation of alkyl chlorides or dehydration, isomerization, or polymerization side reactions may result. Sulfonic acids, such as benzenesulfonic acid, toluenesulfonic acid, or methanesulfonic acid, are widely used in plant operations because of their less corrosive nature. Phosphoric acid is sometimes employed, but it leads to rather slow reactions. Soluble or supported metal salts minimize side reactions but usually require higher temperatures than strong acids. 

Orotic acid (971) has a chequered history. It was isolated in 1905 from the whey of cows milk in Italy and it was subsequently synthesized in the United States in 1907. However, the workers involved were discouraged by some difference in melting points and no direct comparison of specimens was ever made. To make matters worse, the same laboratories prepared the isomeric 5-hydroxy-2-oxo-l,2-dihydropyrimidine-4-carboxylic acid and announced it as orotic acid, again without any direct comparison. Only in 1930 did a German worker actually compare directly natural and the original synthetic orotic acid, thereby showing them to be identical (30CB1000). 

The purpose of this section is to provide guidehnes for this preparation. General aspects are covered. Preparations for the specific units can be drawn from these. Topics include analyst, model, plant, and laboratory preparation. Since no individual analyst can be responsible for all of these activities, communication with other personnel is paramount for the success of the analysis. 

The laboratory preparation of the Udel-type polymer has been described. Bis-phenol A is mixed with chlorobenzene (solvent) and dimethyl sulphoxide (active solvent) and heated to 60°C to obtain a clear solution. Air is displaced from the system by nitrogen or argon and an aqueous solution of caustic soda added. This results in a two-phase system, one predominantly chlorobenzene the... 

The Balz-Schiematin reaction, thermal decomposition of arenediazoniuin fluoroborates, is still a favorite approach to the laboratory preparation of fluoro aromatics [16, 17] Caution must be exercised in handling and decomposing nitroarenediazonium fluoroborates and pyridinediazonium fluoroborates because detonations have been reported [I, 19]... 

Such processes are now no longer used except in the laboratory preparation of D2O2, e.g. ... 

HCIO2 is formed (together with HCIO3) during the decomposition of aqueous solutions of CIO2 (p. 847) but the best laboratory preparation is to treat an aqueous suspension of Ba(C102)2 with... 

Base metals frequently are used in nonsupported form, but noble metals rarely are, except in laboratory preparations. Supporting the noble metals makes a more efficient catalyst on a weight of metal basis and aids in recovery of the metal. Neither of these factors is of much importance in experimental work, but in industrial processing both have significant impact on economics. 

Materials, such as activated carbons, that are derived from natural products differ greatly in their effectiveness when used as catalyst supports, but it is difficult to delimit the factors present in the carbon that influence performance, Certain broad statements, such as that carbons with excessive sulfur or ash content tend to make inferior catalysts, only begin to touch on the problem. One of the advantages of buying commercial catalysts, instead of using laboratory preparations, is that commercial suppliers have solved this problem already by empirical testing of many carbons. They provide catalysts that are best by test. 

Chloroaluminate laboratory preparations proved to be easily extrapolated to large scale. These chloroaluminate salts are corrosive liquids in the presence of protons. When exposed to moisture, they produce hydrochloric acid, similarly to aluminium chloride. However, this can be avoided by the addition of some proton scavenger such as alkylaluminium derivatives. In Difasol technology, for example, carbon-steel reactors can be used with no corrosion problem. 

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