Isoprene
| Structural formula | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||
| General | ||||||||||||||||
| Surname | Isoprene | |||||||||||||||
| other names |
2-methyl-1,3-butadiene |
|||||||||||||||
| Molecular formula | C 5 H 8 | |||||||||||||||
| Brief description |
colorless, extremely flammable liquid with a mild odor |
|||||||||||||||
| External identifiers / databases | ||||||||||||||||
|
||||||||||||||||
| properties | ||||||||||||||||
| Molar mass | 68.12 g mol −1 | |||||||||||||||
| Physical state |
liquid |
|||||||||||||||
| density |
0.68 g cm −3 |
|||||||||||||||
| Melting point |
−146 ° C |
|||||||||||||||
| boiling point |
34 ° C |
|||||||||||||||
| Vapor pressure |
|
|||||||||||||||
| solubility |
|
|||||||||||||||
| Refractive index |
1.4218 |
|||||||||||||||
| safety instructions | ||||||||||||||||
|
||||||||||||||||
| MAK |
Switzerland: 3 ml m −3 or 8.5 mg m −3 |
|||||||||||||||
| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C | ||||||||||||||||
Isoprene is the common name for the unsaturated hydrocarbon 2-methylbuta-1,3-diene. It is a derivative of 1,3-butadiene . Isoprene is the basic unit of the terpenes , but is usually not counted among them. Isoprene is produced by many plants and released into the earth's atmosphere . It is adjacent to methane the hydrocarbon with the highest emission rate.
history
In 1860 Charles Hanson Greville Williams isolated the decomposition products of natural rubber by distillation and called the lightest "isoprene". The structural formula came from William A. Tilden (1882), who also found isoprene in turpentine oil. Hermann Staudinger (1920) had correct ideas about the structure of natural rubber from isoprene , although he had a forerunner in Samuel Pickles (1906).
synthesis
There are a variety of syntheses for isoprene. Ethene reacts with propene to form 2-methyl-1-butene . 2-methylbutene is dehydrogenated to isoprene over chromium oxide-aluminum oxide catalysts .
Another possibility is the dimerization of propene to 2-methyl-1-pentene and the subsequent elimination of methane :
Further syntheses are z. B. the thermolysis of turpentine (in the isoprene lamp according to CH Arries) or the pyrolysis of dipentene or limonene . The most frequently used synthesis is the acid-catalyzed addition reaction of formaldehyde to isobutene via the Prins reaction , which produces 1,3-dioxane , which is split into isoprene in the gas phase at 200 to 300 ° C over an acid catalyst such as phosphoric acid . Another synthesis starting from isobutene and formaldehyde produces 2-methyl-1-buten-4-ol , which is dehydrated at 100 ° C. in a solution of hydrochloric acid and sodium chloride . Isoprene can also be produced from 2-methylbutanal, which is produced by rhodium- catalyzed hydroformylation of 2-butene and subsequent dehydration.
Meaning and occurrence
Isoprene production by plants
Many natural substances can be formally derived from isoprene , which are combined to form isoprenoid natural substances. An example of this are the steroids and terpenes . The direct precursor and starting point of the biosynthesis of isoprenoids is not isoprene, but the biochemically activated isopentenyl pyrophosphate (IPP) and its isomer dimethylallyl pyrophosphate (DMAPP). Isoprene itself is produced by many trees and phytoplankton ; the reason for this is not clear. According to one hypothesis, the gaseous isoprene is supposed to protect the plants from oxidation by ground-level ozone.
A plant whose released isoprene can be set on fire on hot days when there is no wind is diptame ( Dictamnus sp.) (English: gas plant). The plant is not damaged.
Isoprene occurs linked in repeating units in the membranes of the archaea . There they form the hydrophobic parts of the lipids and are linked to glycerine molecules via ether bonds . The isoprene units of the outer and inner layers can combine to form a single lipid layer.
Isoprene in animals
Isoprene is the most common hydrocarbon in human exhaled air. The estimated rate of formation in the human body is 0.15 µmol / (kg · h), corresponding to about 17 mg / day for a person weighing 70 kg. Isoprene is found in low concentrations in many foods.
Isoprene in the atmosphere
Isoprene is released into the atmosphere by plants. The annual emission is around 600 megatons, half of which comes from tropical trees. This corresponds roughly to the annual methane emissions. Isoprene is broken down through the reaction with OH radicals and ozone , creating aldehydes, peroxides and organic nitrates, which can dissolve in droplets or form particles.
properties
Physical Properties
Isoprene is a colorless, low-boiling liquid. The boiling point under normal pressure is 34 ° C. According to Antoine, the vapor pressure function results from log 10 (P) = A− (B / (T + C)) (P in bar, T in K) with A = 4.08822, B = 1108.151 and C = −35.731 in the temperature range from 215.6 to 234.9 K or with A = 3.21586, B = 706.92 and C = −87.046 in the temperature range from 289.9 to 307 K.
Chemical properties
- Isoprene dimerizes to limonene in the sense of a Diels-Alder reaction when heated ; the reaction was first achieved by Gustave Bouchardat in 1878.
- Isoprene is reacted with methyl acrylate in a Diels-Alder reaction to give racemic methyl 4-methylcyclohex-3-en-1-carboxylate. In a Grignard reaction with methylmagnesium bromide (CH 3 MgBr, Grignard reagent ), after hydrolysis, this gives α- terpineol as a racemate :
-Terpinol_Synthesis_V.1.png)
Safety-related parameters
Isoprene forms highly flammable vapor-air mixtures. The compound has a flash point of −54 ° C. The explosion range is between 1% by volume as the lower explosion limit (LEL) and 9.7% by volume as the upper explosion limit (UEL). The maximum explosion pressure is 9.7 bar. The limit gap width was determined to be 0.81 mm (50 ° C). This results in an assignment to explosion group IIB. The ignition temperature is 220 ° C. The substance therefore falls into temperature class T3.
use
The compound can be polymerized to the 'cis' polyisoprene ( isoprene rubber ) and copolymerized with isobutene and acrylonitrile . It is used in organic synthesis for the production of terpene-like structures, as well as for the synthesis of natural products, e.g. B. for α- terpineol .
Safety instructions and toxicology
Isoprene is only of low acute toxicity: the oral LD 50 value for rats is> 2000 mg / kg. Isoprene can be inhaled and ingested. Contact with eyes and skin causes redness and pain, inhalation causes cough, nausea, burning sensation and shallow breath. In animal experiments, isoprene is carcinogenic and mutagenic.
Memory aid
The structural formula of isoprene in the skeletal disc manner can be drawn as a "horse".
Individual evidence
- ↑ a b c d e f g h i j k l m n o Entry on isoprene in the GESTIS substance database of the IFA , accessed on August 13, 2019(JavaScript required) .
- ↑ a b c Entry on isoprene. In: Römpp Online . Georg Thieme Verlag, accessed on August 14, 2019.
- ↑ Entry on Isoprene in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ Swiss Accident Insurance Fund (Suva): Limit values - current MAK and BAT values (search for 78-79-5 or isoprene ), accessed on November 2, 2015.
- ^ Article Whinfield, Lexicon of important chemists , Harri Deutsch 1989.
- ↑ a b c d e f Hans Martin Weitz, Eckhard Loser: Isoprene . In: Ullmann's encyclopedia of industrial chemistry , 2012, Wiley-VC, Volume 20, p. 84. doi : 10.1002 / 14356007.a14_627 .
- ↑ Alexander Fleisher, Zhenia Fleisher: Study of Dictamnus gymnostylis. Volatiles and Plausible Explanation of the "Burning Bush" Phenomenon . In: Journal of Essential Oil Research . 16, No. 1 (Jan / Feb), 2004, pp. 1-3. doi : 10.1080 / 10412905.2004.9698634 .
- ↑ Eberhard Breitmaier: Terpenes: flavors, fragrances, pharmaceuticals, pheromones . Wiley-VCH, 2005, ISBN 978-3-527-31498-0 ( biosynthesis in the Google book search).
- ↑ David Gelmont, Robert A. Stein, James F. Mead: Isoprene - the main hydrocarbon in human breath . In: Biochemical and Biophysical Research Communications . 99, No. 4, 1981, pp. 1456-1460. doi : 10.1016 / 0006-291X (81) 90782-8 .
- ↑ Julian King, Helin Koc, Karl Unterkofler, Paweł Mochalski, Alexander Kupferthaler, Gerald Teschl, Susanne Teschl, Hartmann Hinterhuber, Anton Amann: Physiological modeling of isoprene dynamics in exhaled breath . In: Journal of Theoretical Biology . 267, No. 4, 2010, pp. 626-637. arxiv : 1010.2145 . doi : 10.1016 / j.jtbi.2010.09.028 . PMID 20869370 .
- ↑ Detlev Möller: Air: chemistry, physics, biology, cleanliness, law . de Gruyter, 2003, ISBN 978-3-11-016431-2 ( issue volume in the Google book search).
- ↑ Robert Guderian: Handbook of environmental changes and ecotoxicology . Springer, 2000, ISBN 978-3-540-66184-9 ( breakdown of isoprene in the Google book search).
- ↑ Le Fevre, RJW; Sundaram, A .; Pierens, RK: Molecular Polarisability : the Anisotropy of the Carbon-Oxygen Link in J. Chem. Soc. , 1963, 479-488.
- ↑ Osborn, Ann G .; Douslin, Donald R .: Vapor pressure relations for the seven pentadienes in J. Chem. Eng. Data 14 (1969) 208-209, doi : 10.1021 / je60041a010 .
- ↑ Gubkov, AN; Fermor, NA; Smirnov, NI: Vapor Pressure of Mono-Poly Systems in Zh. Prikl. Khim. (Leningrad) 37 (1964) 2204-2210.
- ↑ a b c E. Brandes, W. Möller: Safety-related parameters. Volume 1: Flammable Liquids and Gases. Wirtschaftsverlag NW - Verlag für neue Wissenschaft, Bremerhaven 2003.