Molecular weight of amines

Picric acid and the picrate salts of amines absorb at 380 nm with a molar absorptivity of 13,400. An accuracy of +2% was obtained for the spectrophotometric determination of molecular weights of amines [30]. Molecular-weight determinations have been reported of sugars from the absorption spectra of their osazones... 

Molecular weight of amine Number of active hydrogens... 

Amine equivaient weight n. Molecular weight of amine divided by the number of... 

Molecular weights of amine picrates, sugars, and many aldehyde and ketone compounds have been determined by this method. The method has an accuracy of 2%. Molecular weights of only small molecules may be determined by this method. 

FIGURE 6.42 The effective molecular weight of amines is increased through association and hydrogen bonding. 

When an amine, or a solution of its hydrochloride, is added to an aqueous solution of chloroplatinic acid, a salt of the base with the cliloroplatinic acid, of general formula BjiHiPtCle (where B is one molecule of the base) is formed and usually crystallises out, for these chloroplatinates hai e normally a rather low solubility in cold water. The chloroplatinate can be filtered off, dried, and then analysed by direct ignition, when only the metallic platinum ultimately remains. Knowing the percentage of platinum in the chloroplatinate, the molecular weight of the latter, and hence of the constituent base, can readily be calculated. 

If the molecular weight of the aniline is known, the number of amino groups can be calculated alternatively, if the aniline is known to be a monacidic base, its molecular weight can be calculated. If the molecular weight and the acidity of the aniline are both known, then dearly the method can be used to estimate the amount of aniline in a given sample. The method is general for many primary and secondary amines, aniline being used solely as a typical member of the former class. 

The method can therefore be used to estimate the percentage of aniline hydrochloride in a crude sample, provided the impurities are not themselves salts of other similar amines. Alternatively, if aniline is known to be a monacidic base (forming therefore a mono-hydrochloride) the molecular weight of aniline can be determined, since the molecular weight of the aniline hydrochloride is clearly that weight which is neutralised by 1000 ml. of vl/.NaOH solution. 

Information on the production levels of the perfluoroethers and perfluorotertiary amines is not disclosed, but the products are available commercially and are marketed, for instance, as part of the Fluorinert Electronic Liquids family by 3M Co. (17). These Hquids have boiling points of 30—215°C with molecular weights of about 300—800. They range in price from 26—88/kg. Perfluoropropene oxide polyethers are marketed by Du Pont with the trade name Krytox (29). The linear perfluoropropene oxide polyethers are marketed by Daikin under the trade name Demnum (28). The perfluoropolyethers derived from photooxidation are marketed by Montefluos under the trade name of Fomblin (30). These three classes of polyethers are priced from about 100—150/kg. 

Lubrication oil additives represent another important market segment for maleic anhydride derivatives. The molecular stmctures of importance are adducts of polyalkenyl succinic anhydrides (see Lubrication and lubricants). These materials act as dispersants and corrosion inhibitors (see Dispersants Corrosion and corrosion control). One particularly important polyalkenyl succinic anhydride molecule in this market is polyisobutylene succinic anhydride (PIBSA) where the polyisobutylene group has a molecular weight of 900 to 1500. Other polyalkenes are also used. Polyalkenyl succinic anhydride is further derivatized with various amines to produce both dispersants and corrosion inhibitors. Another type of dispersant is a polyester produced from a polyalkenyl succinic anhydride and pentaerythritol [115-77-5]. 

An excess of crotonaldehyde or aUphatic, ahcyhc, and aromatic hydrocarbons and their derivatives is used as a solvent to produce compounds of molecular weights of 1000—5000 (25—28). After removal of unreacted components and solvent, the adduct referred to as polyester is decomposed in acidic media or by pyrolysis (29—36). Proper operation of acidic decomposition can give high yields of pure /n j ,/n7 j -2,4-hexadienoic acid, whereas the pyrolysis gives a mixture of isomers that must be converted to the pure trans,trans form. The thermal decomposition is carried out in the presence of alkaU or amine catalysts. A simultaneous codistillation of the sorbic acid as it forms and the component used as the solvent can simplify the process scheme. The catalyst remains in the reaction batch. Suitable solvents and entraining agents include most inert Hquids that bod at 200—300°C, eg, aUphatic hydrocarbons. When the polyester is spHt thermally at 170—180°C and the sorbic acid is distilled direcdy with the solvent, production and purification can be combined in a single step. The solvent can be reused after removal of the sorbic acid (34). The isomeric mixture can be converted to the thermodynamically more stable trans,trans form in the presence of iodine, alkaU, or sulfuric or hydrochloric acid (37,38). 

This process is based on the very high reactivity of the isocyanate group toward hydrogen present ia hydroxyl groups, amines, water, etc, so that the chain extension reaction can proceed to 90% yield or better. Thus when a linear polymer is formed by chain extension of a polyester or polyether of molecular weight 1000—3000, the final polyurethane may have a molecular weight of 100,000 or higher (see Urethane polymers). 

To determine the rate behavior of chain growth polymerization reactions, we rely on standard chemical techniques. We can choose to follow the change in concentration of the reactive groups, such as the carboxylic acid or amine groups above, with spectroscopic or wet lab techniques. We may also choose to monitor the average molecular weight of the sample as a function of time. From these data it is possible to calculate the reaction rate, the rate constant, and the order of the reacting species. 

Figure 9.2. Chromatogram of a seawater extract (20 ml) sample for amino acids collected at 6 m in the Kiel Fjord. The concentrations of the individual acids were quantified as follows (in nmol/1) meto, 11 asp 34.4 thr, 23.2 ser, 88 glu, 36 gly, 100 ala, 56 vol, 16 ileu, 9.6 leu, 12 galactosamine and amino sugars, 4 tyr, 6.8 phe, 7.2 B-ala, 20.8 a-amino-y, 14.4 orn, 44 lys, 12 hist, 7.2 arg, 8.6 cysS02H, 4 cit, trace tan, cys, trace glucose-amine, trace met, trace urea, trace phosphoserine, trace OH-lys, trace. The total concentration of amino acid in the sample lies around 51 q.g/1, assuming a mean molecular weight of 100. Source [264]...

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