Truxillic acid

Truxillic acids are any of several crystalline stereoisomeric cyclic dicarboxylic acids with the formula (C₆H₅C₂H₂(CO₂H)₂. They are colorless solids. These compounds are obtained by the [2 + 2] photocycloadditions of cinnamic acid where the two trans alkenes react head-to-tail. The isolated stereoisomers are called truxillic acids.^[1] The preparation of truxillic acids provided an early example of organic photochemistry.^[2]

Cinnamic Acid CycloAddition

Truxillic acid

Names
IUPAC name 7,8′-Cyclo-8,7′-neolignane-9,9′-dioic acid
Systematic IUPAC name 2,4-Diphenylcyclobutane-1,3-dicarboxylic acid
Identifiers
CAS Number	4462-95-7 Y
3D model (JSmol)	Interactive image
ChemSpider	70589
ECHA InfoCard	100.022.478
PubChem CID	78213
UNII	821BB4R21V Y
CompTox Dashboard (EPA)	DTXSID20196252
SMILES OC(C1C(C2=CC=CC=C2)C(C(O)=O)C1C3=CC=CC=C3)=O
Properties
Chemical formula	C18H16O4
Molar mass	296.322 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Occurrence and reactions

These compounds are found in a variety of plants, for example in coca.^[3][4] Incarvillateine, an alkaloid from the plant Incarvillea sinensis, is a derivative of α-truxillic acid.

Upon heating, truxillic acids undergo cracking to give cinnamic acid.^[5]

Isomers

Truxillic acid can exist in five stereoisomers.^[6][7]

Truxillic acid isomers

Isomer	a	b	c	d	e	f
α-truxillic acid (cocaic acid[8])	COOH	H	H	C6H5	H	COOH
γ-truxillic acid	COOH	H	H	C6H5	COOH	H
ε-truxillic acid	H	COOH	C6H5	H	H	COOH
peri-truxillic acid	COOH	H	C6H5	H	COOH	H
epi-truxillic acid	COOH	H	C6H5	H	H	COOH

Below are the five stereoisomers of truxillic acid, called alpha, gamma, epsilon, peri, and epi. These are shown both in a 2D skeletal diagram with stereocenters indicated and a 3D rendering of the structural geometry of the isomers themselves.

See also

• Truxinic acids are isomers of the truxillic acids with phenyl groups on adjacent methyne centers.