Maleic anhydride

Maleic anhydride is a planar molecule. By virtue of the acid anhydride group, the alkene is electrophilic.

On account of its cycle of 4 π electrons in an array of 5 atoms with p orbitals, maleic anhydride was long thought to exhibit antiaromaticity. However, a thermochemical study concluded that only 8 kJ/mol of destabilization energy can be ascribed to this effect, making it weakly antiaromatic at best.{{Cite journal|last1=Roux|first1=María Victoria|last2=Jiménez|first2=Pilar|last3=Martín-Luengo|first3=Maria Ángeles|last4=Dávalos|first4=Juan Z.|last5=Sun|first5=Zhiyuan|last6=Hosmane|first6=Ramachandra S.|last7=Liebman|first7=Joel F.|date=May 1997|title=The Elusive Antiaromaticity of Maleimides and Maleic Anhydride: Enthalpies of Formation of N-Methylmaleimide, N-Methylsuccinimide, N-Methylphthalimide, and N-Benzoyl-N-methylbenzamide|journal=The Journal of Organic Chemistry|language=en|volume=62|issue=9|pages=2732–2737|doi=10.1021/jo9621985|pmid=11671632|issn=0022-3263}}

Maleic anhydride is produced by vapor-phase oxidation of n-butane. The overall process converts the methyl groups to carboxylate and dehydrogenates the backbone. The selectivity of the process reflects the robustness of maleic anhydride, with its conjugated double-bond system. Traditionally maleic anhydride was produced by the oxidation of benzene or other aromatic compounds. As of 2006, only a few smaller plants continue to use benzene.

In both cases, benzene and butane are fed into a stream of hot air, and the mixture is passed through a catalyst bed at high temperature. The ratio of air to hydrocarbon is controlled to prevent the mixture from igniting. Vanadium pentoxide and molybdenum trioxide are the catalysts used for the benzene route, whereas vanadium phosphate is used for the butane route:

:{{chem2|C4H10 + 3.5 O2 -> C4H2O3 + 4 H2O}} ∆H = −1236 kJ/mol

The main competing process entails full combustion of the butane, a conversion that is twice as exothermic as the partial oxidation.

The traditional method using benzene became uneconomical due to the high and still rising benzene prices and by complying with the regulations of benzene emissions. In addition, in the production of maleic anhydride (4 C-atoms) a third of the original carbon atoms is lost as carbon dioxide when using benzene (6 carbon atoms). The modern catalytic processes start from a 4-carbon molecule and only attaches oxygen and removes water; the 4-C-base body of the molecule remains intact. Overall, the newer method is therefore more material efficient.{{cite book |last1=Philipp |first1=Bertram |last2=Stevens |first2=Peter |title=Grundzüge der industriellen Chemie: ein einführendes Lehr- u. Lernbuch |date=1987 |publisher=VCH-Verl.-Ges |location=Weinheim |isbn=3-527-25991-0 |page=S. 179}}

Parallels exist with the production of phthalic anhydride: While older methods use naphthalene, modern methods use o-xylene as feedstock.

File:MAderivs.svg from dimerization using 2-aminopyridine as catalyst, tetrachlorolactone from treatment with phosphorus pentachloride, product of AlCl₃-catalyzed acylation of benzene, and product of ene reaction with propylene.]]

The chemistry of maleic anhydride is very rich, reflecting its ready availability and bifunctional reactivity. Maleic anhydride hydrolyzes, producing maleic acid, {{chem2|cis\sHOOC\sCH\dCH\sCOOH}}. With alcohols, the half-ester is generated, e.g., {{chem2|cis\sHOOC\sCH\dCH\sCOOCH3}}. With amines, maleic anhydride gives maleamic acids.{{cite book |doi=10.1002/0471238961.1301120506051220.a01.pub3 |chapter=Maleic Anhydride, Maleic Acid, and Fumaric Acid |title=Kirk-Othmer Encyclopedia of Chemical Technology |date=2024 |last1=Hood |first1=David K. |pages=1–51 |isbn=978-0-471-48494-3 }}

Maleic anhydride is a classic substrate for Diels-Alder reactions.{{cite journal |author1=Samuel Danishefsky |author2=Takeshi Kitahara |author3=Paul F. Schuda |name-list-style=amp | title=Preparation and Diels-Alder Reaction of a Highly Nucleophilic Diene: trans-1-Methoxyl-3-Trimethylsiloxy-1,3-Butadiene and 5β-Methoxycyclohexan-1-one-3β,4β-Dicarboxylic acid Andhydride |journal=Org. Synth. |year=1983 |volume=61 |page=147 |doi=10.1002/0471264180.os061.30|isbn=978-0-471-26422-4}} It was used for work in 1928, on the reaction between maleic anhydride and 1,3-butadiene, for which Otto Paul Hermann Diels and Kurt Alder were awarded the Nobel Prize in 1950. It is through this reaction that maleic anhydride is converted to many pesticides and pharmaceuticals. Their 1928 patent also provided many other examples of reactions involving maleic anhydride, such as the reaction with cyclopentadiene to form nadic anhydride.{{cite patent |country=United States |number=US1944731A |title=Organic compound having hydrogenated ring systems and process of preparing it |pubdate=January 23, 1934 |gdate=01-23-1934 |fdate= |pridate=11-05-1927 |invent1=Otto Diels |invent2=Kurt Alder |status=Expired |url=https://worldwide.espacenet.com/patent/search/family/007750680/publication/US1944731A?q=US1944731}}

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At higher temperatures, the half salts, half esters of maleic acid undergo the Michael reaction with active methylene or methine compounds such as malonate or acetoacetate esters in the presence of sodium acetate catalyst. These intermediates were used for the same Krebs cycle intermediates aconitic and isocitric acids.{{cite patent| country=United States |number=US4146543A |invent1=E.Gutierrez |status=Expired |title=Reaction of maleic anhydride with active methylene or methine containing compounds |pubdate=03-27-1979 |gdate=03-27-1979 |fdate=11-04-1977 |pridate=11-04-1977 |assign1=Lever Brothers Company, New York, N.Y. |url=https://patents.google.com/patent/US4146543A/en}}{{cite patent |country=United States |number=US4123458A |invent1=E.Gutierrez |invent2=V.Lamberti |status=Expired |title=Preparation of cis and trans aconitic acids and their salts |pubdate=10-31-1978 |gdate=10-31-1978 |fdate=12-22-1975 |pridate=12-22-1975 |assign1=Lever Brothers Company, New York, N.Y. |url=https://patents.google.com/patent/US4123458A/en}}

Maleic anhydride dimerizes in a photochemical reaction to form cyclobutane tetracarboxylic dianhydride (CBTA). This compound is used in the production of polyimides and as an alignment film for liquid crystal displays.{{Cite journal |doi=10.1021/op900306z |title=Photodimerization of Maleic Anhydride in a Microreactor Without Clogging |year=2010 |last1=Horie |first1=T. |last2=Sumino |first2= M. |last3=Tanaka |first3=T. |last4=Matsushita |first4=Y. |last5=Ichimura |first5=T. |last6=Yoshida |first6=J.I. |journal=Organic Process Research & Development |issue=2 |volume=14|pages=405–410 }}

:File:MaleicAnhydrideDimerization.svg

It is also a ligand forming metal-alkene complexes, examples being {{chem2 |Pt(PPh3)2(MA)}} and {{chem2 |Fe(CO)4(MA)}}.{{cite journal |doi=10.1002/hlca.19630460128 |title=π-Olefin-eisentetracarbonyl-Komplexe mit Liganden der Malein-, Fumar-, Acryl-, Methacryl- und Zimtsäure-Reihe |date=1963 |last1=Weiss |first1=E. |last2=Stark |first2=K. |last3=Lancaster |first3=J. E. |last4=Murdoch |first4=H. D. |journal=Helvetica Chimica Acta |volume=46 |pages=288–297 }}

Malathion.png|Malathion is a popular insecticide derived from maleic anhydride

SulfosuccinateRR'.png|Sodium sulfosuccinate esters, common class of surfactants derived from maleic anhydride

AlkylsuccinicAnhydrideC18again.png|Alkenylsuccinic anhydrides, which are derived from maleic anhydride, are widely used in papermaking

Rubratoxin A.png|Rubratoxin A is one of many natural products containing a maleic anhydride-like subunit.

Around 50% of world maleic anhydride output is used in the manufacture of unsaturated polyester resins (UPR).{{citation needed|date=May 2025}} These resins are used in diverse applications such as vehicles, construction, furniture, and machinery.{{cite report|publisher=U.S. Environmental Protection Agency|year=1983|section-url=https://www.epa.gov/sites/default/files/2020-10/documents/c06s14.pdf|section=6.14 Maleic Anhydride|title=AP-42: Compilation of Air Emissions Factors from Stationary Sources}} Chopped glass fibers are added to UPR to produce fiberglass reinforced plastics.

Maleic anhydride is hydrogenated to 1,4-butanediol (BDO), used in the production of thermoplastic polyurethanes, elastane/Spandex fibers, polybutylene terephthalate (PBT) resins and many other products.{{citation needed|date=May 2025}}

{{More citations needed section|date=June 2025}}

Diels-Alder reaction of maleic anhydride and butadiene and isoprene gives the respective tetrahydrophthalic anhydrides which can be hydrogenated to the corresponding hexahydrophthalic anhydrides. These species are used as curing agents in epoxy resins.{{Cite web |last=Hara |first=Osamu |date=December 20, 1990 |title=Technical News #32: Curing Agents for Epoxy Resin |url=https://www.threebond.co.jp/en/technical/technicalnews/pdf/tech32.pdf |url-status=live |archive-url=https://web.archive.org/web/20250608051424/https://www.threebond.co.jp/en/technical/technicalnews/pdf/tech32.pdf |archive-date=June 8, 2025 |website=Three Bond Co., LTD.}} Another market for maleic anhydride is lubricating oil additives, which are used in gasoline and diesel engine crankcase oils as dispersants and corrosion inhibitors. Changes in lubricant specifications and more efficient engines have had a negative effect on the demand for lubricating oil additives, giving flat growth prospects for maleic anhydride in this application.

A number of smaller applications exist for maleic anhydride. Personal care products consuming maleic anhydride include hair sprays, adhesives and floor polishes. Maleic anhydride is also a precursor to compounds used for water treatment detergents, insecticides and fungicides, pharmaceuticals, and other copolymers.

The maleic anhydride group occurs in several natural products, some of which show promising therapeutic or pesticidal activity.{{cite journal |doi=10.1021/cr050029r |title=Natural Products with Maleic Anhydride Structure: Nonadrides, Tautomycin, Chaetomellic Anhydride, and Other Compounds |date=2007 |last1=Chen |first1=Xiaolong |last2=Zheng |first2=Yuguo |last3=Shen |first3=Yinchu |journal=Chemical Reviews |volume=107 |issue=5 |pages=1777–1830 |pmid=17439289 }} In the wood science, maleic anhydride in combination with other agents, has been used for protection and modification of wood in order to improve its material properties.{{cite journal | last=Zheng | first=Dingyuan | last2=Li | first2=Zehuai | last3=Yao | first3=Wenrui | last4=Wang | first4=Yuning | last5=Sun | first5=Ce | last6=Tan | first6=Haiyan | last7=Zhang | first7=Yanhua | title=A maleic anhydride-mediated green and sustainable route for versatile wood platform | journal=Chemical Engineering Journal | publisher=Elsevier BV | volume=479 | year=2024 | issn=1385-8947 | doi=10.1016/j.cej.2023.147907 | page=147907}}{{cite journal | last=Kim | first=Injeong | last2=Ross | first2=Lone | last3=Alfredsen | first3=Gry | last4=Karlsson | first4=Olov | last5=Kaynak | first5=Elif | last6=Das | first6=Oisik | last7=Jones | first7=Dennis | last8=Mantanis | first8=George I. | last9=Sandberg | first9=Dick | author8-link=George Mantanis |author9-link=Dick Sandberg |title=Enhancement of Biological Durability and Fire Safety in Wood Modified with Maleic Anhydride and Sodium Hypophosphite | journal=Forests | publisher=MDPI AG | volume=16 | issue=3 | date=2025-03-16 | issn=1999-4907 | doi=10.3390/f16030526 | doi-access=free | page=526}}

Source: Kirk & Othmer {{full citation needed|date=September 2014}}

{{unref section|date=March 2025}}

Liquid maleic anhydride is available in road tankers and/or tank-containers which are made of stainless steel, which are insulated and provided with heating systems to maintain the temperature of {{convert|65-75|C|F}}. Tank cars must be approved for the transport of molten maleic anhydride.

Liquid/molten maleic anhydride is a dangerous material in accordance with RID/ADR.

Solid maleic anhydride pellets are transported by trucks. Packaging is generally in {{convert|25|kg|lb|abbr=on}} polyethylene bags.

This compound poses relatively low-risk environmental hazards, an important feature for some applications. In humans, exposure to maleic anhydride may cause irritation to the respiratory tract, eyes, exposed mucosa, and skin. Maleic anhydride is also a skin and respiratory sensitizer.{{cite web |url=http://echa.europa.eu/documents/10162/9801478/sev1_203_571_6_report_en.pdf |title=Substance Evaluation Report: Maleic anhydride |publisher=Environment Agency Austria |access-date=2014-10-13 |archive-url=https://web.archive.org/web/20141018174452/http://echa.europa.eu/documents/10162/9801478/sev1_203_571_6_report_en.pdf |archive-date=2014-10-18 |url-status=dead}}

Maleic anhydride is a low hazard profile chemical. Maleic anhydride rapidly hydrolyzes to form maleic acid in the presence of water and hence environmental exposures to maleic anhydride itself are unlikely. Maleic acid is biodegradable under aerobic conditions in sewage sludge as well as in soil and water.

Food starch for use in night markets sold from a supplier in Tainan city, Taiwan, were found to contain maleic anhydride in December 2013. The supplier was investigated regarding the {{convert|300|t|ST|abbr=on}} of tainted starch; an earlier inspection in November had found {{convert|32|t|ST|abbr=on}}.{{cite news |url=http://www.wantchinatimes.com/news-subclass-cnt.aspx?id=20131219000005&cid=1103 |title=Tainted starch found in Tainan yet again |publisher=Want China Times |date=2013-12-19 |access-date=2013-12-19 |archive-url=https://web.archive.org/web/20131219152045/http://www.wantchinatimes.com/news-subclass-cnt.aspx?id=20131219000005&cid=1103 |archive-date=2013-12-19 |url-status=dead }}

{{reflist}}

• {{ICSC|0799|07}}
• {{PGCH|0376}}
• [https://web.archive.org/web/20070611162734/http://www.oehha.ca.gov/air/chronic_rels/pdf/maleic.pdf Chronic toxicity summary]
• [http://www.osha.gov/dts/sltc/methods/organic/org086/org086.html Maleic anhydride at Occupational Safety & Health Administration]

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Category:Carboxylic anhydrides

Category:Furanones