Handbook of Solvents - George Wypych - ChemTech - Ventech!

15.1 Standard methods of solvent analysis 1065
organic halides. After decomposing the excess reagent with water, the separated aqueous
phase is titrated in presence of acetone with a silver nitrate solution. Organic chlorides present
in aromatic hydrocarbons can also be determined by microcoulometry. 93 The presence
of chlorine compounds may adversely affect equipment and/or reaction therefore their concentration
is frequently controlled. A liquid specimen is injected into a combustion tube
maintained at 900 o C, converted to hydrogen halides, and carried by a carrier gas (50% oxygen,
50% argon) to a titration cell where it reacts with silver ions in the electrolyte.
The determination of peroxides has two goals: one is to monitor peroxide concentration
used as initiator and catalysts and the other is to detect formation of hazardous peroxides
formed as autoxidation products in ethers, acetals, dienes, and alkylaromatic
hydrocarbons. A sample is dissolved in a mixture of acetic acid and chloroform. The solution
is deaerated and potassium iodide reagent is added and let to react for1hindarkness. 94
The iodine formed in reaction is measured by absorbance at 470 nm and result calculated to
active oxygen in the sample. The method can determine hydroperoxides, peroxides,
peresters, and ketone peroxides. Oxidizing and reducing agents interfere with the determination.
Mercaptans in motor fuels, kerosene and other petroleum products can be detected by
shaking the liquid sample with sodium plumbite solution, adding powdered sulfur and shaking
again. 95 If a mercaptan or hydrogen sulfide is present, discoloration of the floating sulfur
or liquid phase occurs.
The nonvolatile content of a halogenated solvent is determined by drying the sample
in a platinum evaporating dish at 105 o C. 96 Depending on boiling point and the concentration
of nonvolatile matter three alternate procedures are proposed.
The Karl Fisher method is recommended for general use in solvents to determine the
water content. 97 It is not suitable if mercaptans, peroxides, or appreciable quantities of aldehydes
and amines are present. Water in halogenated solvents may cause corrosion, spotting,
reduce shelf-life of aerosols, or inhibit chemical reactions, thus special method, also based
on the Karl Fischer titration, was developed for halogenated solvents. 98
The titration of ionizable chlorides with mercuric acetate solution in the presence of
s-diphenylcarbazone as an indicator is used to determine chloride in
trichlorotrifluoroethane. 99 A visual appearance test to detect admixtures in halogenated solvents
is based on the observation of suspended particles, sediment, turbidity and free floating
water. 100
The aromatic content of hydrocarbon mixture is estimated from the determination of
aniline point. 101 Aromatic hydrocarbons have the lowest and paraffins the highest aniline
points. Cycloparaffins and olefins are between the two. Aniline point increases as the molecular
weight increases. A mixture of specific aniline and solvent is heated at a controlled
rate until it forms one phase. The mixture is then cooled and the temperature at which the
miscible liquid separates into two phases is determined. Four methods are discussed in the
standard 101 suitable for transparent, non-transparent, easily vaporizing, and measured in
small quantities.
The presence of oxidizable materials in acetone and methanol that are associated with
contaminations during manufacture and distribution can be evaluated by permanganate
time. 102 Oxidizable contaminants may adversely affect catalysts or ligand complexes which
are sensitive to oxidation. Oxidizable substances reduce potassium permanganate to manganese
oxide which is yellow. The method is designed to measure the time required to
change color to the color of a standard.
Small admixtures of acetone in methanol (more than 0.003 wt%) can be detected after
a reaction with Nessler’s reagent. 103 The reacted sample is compared with a standard, which
contains 0.003 wt% acetone and the difference in turbidity is reported.