Solvent
[2] Specific uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene); as paint thinners (toluene, turpentine); as nail polish removers and solvents of glue (acetone, methyl acetate, ethyl acetate); in spot removers (hexane, petrol ether); in detergents (citrus terpenes); and in perfumes (ethanol).
This arrangement is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding, dipole moment and polarizability.
[6] Heuristically, the dielectric constant of a solvent can be thought of as its ability to reduce the solute's effective internal charge.
The Grunwald–Winstein mY scale measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction.
Similarly, water and hexane (or vinegar and vegetable oil) are not miscible with each other and will quickly separate into two layers even after being shaken well.
Another option, Hansen solubility parameters, separates the cohesive energy density into dispersion, polar, and hydrogen bonding contributions.
Solvents with a dielectric constant (more accurately, relative static permittivity) greater than 15 (i.e. polar or polarizable) can be further divided into protic and aprotic.
Protic solvents, such as water, solvate anions (negatively charged solutes) strongly via hydrogen bonding.
Rational substitutions can also be made for "good" solvents (effective at dissolving the solute) that are "bad" (expensive or hazardous to health or the environment).
[14][15] A 1:1 mixture of toluene and 1,4 dioxane has δD, δP and δH values of 17.8, 1.6 and 5.5, comparable to those of chloroform at 17.8, 3.1 and 5.7 respectively.
Small amounts of low-boiling-point solvents like diethyl ether, dichloromethane, or acetone will evaporate in seconds at room temperature, while high-boiling-point solvents like water or dimethyl sulfoxide need higher temperatures, an air flow, or the application of vacuum for fast evaporation.
Important exceptions are most of the halogenated solvents like dichloromethane or chloroform will sink to the bottom of a container, leaving water as the top layer.
This is crucial to remember when partitioning compounds between solvents and water in a separatory funnel during chemical syntheses.
Multicomponent solvents appeared after World War II in the USSR, and continue to be used and produced in the post-Soviet states.
Solvent vapors are heavier than air; they will sink to the bottom and can travel large distances nearly undiluted.
Both diethyl ether and carbon disulfide have exceptionally low autoignition temperatures which increase greatly the fire risk associated with these solvents.
The autoignition temperature of carbon disulfide is below 100 °C (212 °F), so objects such as steam pipes, light bulbs, hotplates, and recently extinguished bunsen burners are able to ignite its vapors.
[22][23] This can delay or prevent the timely recognition of a dangerous fire, until flames spread to other materials.
The process of peroxide formation is greatly accelerated by exposure to even low levels of light, but can proceed slowly even in dark conditions.
Unless a desiccant is used which can destroy the peroxides, they will concentrate during distillation, due to their higher boiling point.
Minor mechanical disturbances, such as scraping the inside of a vessel, the dislodging of a deposit, or merely twisting the cap may provide sufficient energy for the peroxide to detonate or explode violently.
[24] A number of tests can be used to detect the presence of a peroxide in an ether; one is to use a combination of iron(II) sulfate and potassium thiocyanate.
[citation needed] Solvents like diethyl ether and chloroform have been used in medicine as anesthetics, sedatives, and hypnotics for a long time.[when?]
The cumulative brain effects of long-term or repeated exposure to some solvents is called chronic solvent-induced encephalopathy (CSE).
[33] Chronic exposure to organic solvents in the work environment can produce a range of adverse neuropsychiatric effects.
Since solvents readily migrate substantial distances, the creation of widespread soil contamination is not uncommon; this is particularly a health risk if aquifers are affected.
