Solvent

Can solve or dilute a solvent ( also solvents or solvent) is a substance of gases, liquids or solids, without this resulting in chemical reactions between the solute and the unattached material. In general, liquids such as water and liquid organic substances used to dissolve other substances. But even solids can dissolve other substances (eg, is dissolved in the hydrogen tank of hydrogen cars hydrogen gas in a solid metal).

Solvent or solvent

Both terms can be found for over 200 years in the literature. In the research laboratory and the field to solvents has been established in the industrial and technical chemicals industry, however solvents. For example, speaks the Rompp Encyclopedia chemistry of solvent while the Technical Rule prefer solvent.

Definition in everyday life

The most commonly used solvent is water. In view of paints, varnishes, adhesives, etc. However, we expect in the term " solvent" to substances that can cause unpleasant odors, health and environmental damage, and explosive vapors. What is meant here are solvent (Technical Rules for Hazardous Substances ) 610, according to which only volatile organic solvents are designated with a boiling point up to 200 ° C as a solvent in the sense of Technical Rule.

The " high boilers " low-volatile substances with boiling points above 200 ° C, are therefore not considered legally as a solvent. While classical solvents are to days completely evaporated within a few hours after processing due to their volatility, the high boiler substitute contained in some " solvent-free " products will be issued under certain circumstances even months or years into the air and therefore are sometimes even more critical assessment than products with classical solvents.

The avoidance of toxic and / or polluting substances is part of Green Chemistry.

Chemistry

Though the solvent does not itself participate in the chemical reaction, usually, it is very important for chemical reactions. The effects of the solvent are varied and depend on the reaction. Through the solution of a substance in a solvent reactions are often enabled in finite time periods, since the shock frequencies arise not sufficiently high reaction rates, eg in solids at low temperatures. The main tasks of the solvent in chemical reactions

• Convective heat and mass transport
• Stabilization of transition states of the reaction
• Dilution in order to avoid side reactions

For the cleaning and processing of reaction mixtures (downstream process) solvent play a more important role. Here are examples of some important procedures named:

• Precipitation
• Crystallization
• Recrystallization
• Extraction
• Chromatography

Market Economics

The main solvent group are alcohols, such as ethanol, n-butanol, isopropanol and methanol. In 2011, approximately 6.4 million tons were in demand thereof world. An above-average increase in consumption of more than 3% per year is expected in the period 2019 to 2011 in ethanol and in the ethers. In addition to the halogenated solvents, which continue their downward trend in Western Europe and North America, including aromatics and pure hydrocarbons will continue to decline in importance in the long term.

Dissolving properties

The quantitative prediction of solvent properties is difficult and often defies intuition. It can be set up general rules, however, can only be regarded as a rough guideline.

Polar substances dissolve well in general in polar solvents (eg salts in water). Non-polar substances dissolve in generally good in nonpolar solvents ( eg, nonpolar organic substances in benzene or ether).

Solvents are usually classified according to their physical properties in classes. Such classification criteria are eg:

• Boiling point
• Permittivity
• Flashpoint
• Volatility
• Viscosity
• Polarity
• CH- acidity

Aprotic solvents

If a molecule does not have a functional group that can be cleaved from the hydrogen atoms in the molecule as a proton ( dissociation), one speaks of an aprotic solvent. These are compared with the protic solvents.

Aprotic nonpolar

Alkanes are nonpolar due to the small difference in electronegativity between carbon and hydrogen. This makes all the substances of these groups into each other easily soluble; they are very lipophilic ( actually even more lipophilic than the very weakly polar, eponymous fats) and very hydrophobic (water- repellent). But not only water can not be solved, but all other strongly polar substances do not, such as short-chain alcohols, hydrogen chloride or salts. In the liquid, the particles are only held together by van der Waals forces. Therefore, in this group of substances covered the boiling temperatures compared to molecular size and mass of much lower than permanent dipoles. Since a detachment of protons to form carbanions with extremely strong bases is possible, they are aprotic. In addition, also included in the group of non-polar aprotic solvent compounds, such as carboxylic acid esters or ethers, although containing polar bonds, because of their low permittivity but which are not able to dissolve ionic compounds.

Representatives of this group are:

• Alkanes ( paraffins)
• Alkenes (olefins ), alkynes
• Benzene and other aromatic compounds with aliphatic and aromatic substituents
• Carboxylic acid esters
• Ethers such as diethyl ether
• Completely symmetrical built molecules such as tetramethylsilane or carbon tetrachloride
• Carbon disulfide and carbon dioxide at high pressure and

• Halogenated hydrocarbons, which are either (such as carbon tetrachloride ) or completely non-polar but despite the high electronegativity of the respective halogen, such as chlorine, only slightly polar ( methylene chloride)

• A special subset of halogenated hydrocarbons form the perfluorinated hydrocarbons (eg hexafluorobenzene ), can be polarized not only himself nonpolar, but also very bad from the outside and therefore rather poor and with the other non-polar solvents tolerated.

Aprotic polar

If the molecule is, however, substituted with strongly polar functional groups such as carbonyl group, a nitro group or the nitrile group, so, the molecule has a dipole moment, between molecularly So now occurs electrostatic attraction permanent dipoles to the still existing (but much weaker ) van der Waals forces added. This results in a substantial increase in the boiling point, and in many cases result in a deterioration in miscibility with non-polar solvents as well as an improvement in the solubility of polar substances and. Typical aprotic polar solvents have a permittivity above 15 and are able to solvate cations. Since the anions are hardly solvated ( naked anions), they show a high SN2 reactivity. Such solvents are well suited to perform nucleophilic substitutions under mild conditions. These include:

• Ketones, such as acetone
• Lactones such as γ -butyrolactone
• Lactams such as N-methyl -2-pyrrolidone
• Nitriles such as acetonitrile
• Nitro compounds such as nitromethane
• Tertiary carboxylic acid amides such as dimethylformamide
• Urea derivatives, such as tetramethylurea or dimethylpropyleneurea ( DMPU )
• Sulfoxides such as dimethyl sulfoxide ( DMSO)
• Sulfones such as sulfolane
• Carbonic acid esters, such as dimethyl carbonate or ethylene carbonate

Protic solvents

Once a molecule has a functional group can be cleaved from the hydrogen atoms in the molecule as a proton ( dissociation), it is called a protic solvent. These are compared to the aprotic solvents.

The main protic solvent is water, the (simplified) into a proton and hydroxide ion dissociates.

Other protic solvents are, for example, alcohols and carboxylic acids dar. Here, the spin-off of the proton always on the OH group because the electronegative oxygen can absorb the resulting negative charge well.

The measure in which dissociated the respective solvent is determined by the acidity ( according to the acid - base concept of Brønsted and Lowry ). It is to be noted that carbon-bonded hydrogen atoms can be eliminated as protons (CH- acidity ), the acidity of these compounds, however, is usually too low to permit an appreciable dissociation in neutral medium. The release of these protons is only possible by very strong bases.

Polar protic solvents dissolve salts and polar compounds, whereas the solubility of nonpolar compounds is low.

Protic solvents are:

• Water is the principle solvent at all, especially in the living world
• Methanol, ethanol and other alcohols ( the larger the carbon backbone, the less pronounced is the polar character, so cholesterol is, for example, an alcohol but still highly lipophilic )
• Primary and secondary amines
• Carboxylic acids ( formic, acetic )
• Primary and secondary amides such as formamide
• Mineral acids (sulfuric acid, hydrogen halides and hydrogen halides )

Table with solvents and their data

Indifferent solvent

Under an indifferent or neutral solvent in polymer chemistry a medium understood the

• Termination and transfer reactions of polymerization and thus also of polymerization and degree little or not affected.
• For all domains of a block copolymer same solution properties (the opposite is a selective solvent).