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Fourteen compounds have been identified as products of the acid catalyzed cyclization of citral under mild aqueous acid conditions. Three major products of the reaction, 1,8-epoxy-p-menth-2-ene (11) and trans- and cis-p-menth-2-ene-1,8-diol (16 and 18) are reported here for the first time as products from citral. Possible mechanistic pathways leading to the products are discussed.

Comets are known to contain ices, organic compounds, and silicate dust grains. During final accretion by the early Earth, comets will have contributed chemical ingredients in several ways: as bulk additions to the volatile inventory; as particles, molecules, radicals, and atoms; and perhaps in rare cases as localized concentrated matter. Having originated in the outer solar system and/or interstellar space, these constituents are, not surprisingly, unique compared to those otherwise found at the surface of the early Earth. Comets are apparently rich in materials that may be vital to successful prebiotic evolution, including light elements, catalytic elements, organic compounds, and microparticles of various types down to the submicrometer size range. Because of their exceptional chemical nature and great abundance, comets deserve serious consideration in models of accretion and early protobiological activity.