Bottom-Up Synthesis of 1,1-Ethenediol (H₂CC(OH)₂)─The Simplest Unsaturated Geminal Diol─In Interstellar Analogue Ices

Abstract

Because of their nucleophilic character and high reactivity, enolsreaction intermediates carrying a hydroxyl group connected to a carbon–carbon double bondplay a key role in the formation of complex organic molecules in astrobiology and biochemistry. Here, we report the first bottom-up preparation of 1,1-ethenediol (H2CC­(OH)2)the simplest unsaturated geminal enol of acetic acid (CH3COOH) and potential precursor for the formation of glycinein interstellar analogue ices of carbon dioxide and methane processed by proxies of galactic cosmic rays. These enols can easily form via nonequilibrium chemistry in low temperature (10 K) interstellar ices at abundances orders of magnitude higher than thermodynamically predicted. These energetically less favorable tautomers remain stable in ice-coated interstellar nanoparticles in molecular clouds and also upon sublimation into the gas phase in star forming regions thus providing the raw material to a complex and exotic organic chemistry under extreme conditions in deep space.

Mechanistical study on the formation of hydroxyacetone (CH3COCH2OH), methyl acetate (CH3COOCH3), and 3-hydroxypropanal (HCOCH2CH2OH) along with their enol tautomers (prop-1-ene-1,2-diol (CH3C(OH)CHOH), prop-2-ene-1,2-diol (CH2C(OH)CH2OH), 1-methoxyethen-1-ol (CH3OC(OH)CH2) and prop-1-ene-1,3-diol (HOCH2CHCHOH)) in interstellar ice analogs

“…3). In addition, keto-enol tautomerization reaction can occur in the irradiated ices as shown previously by Kleimeier et al 16,61 and thus their enol products may also be detected at 10.49 eV. Thereafter, the photon energy was reduced to 9.70 eV; at this energy, isomers/conformers 1b, 2a, and 3a–3c cannot be ionized (Fig.…”

“…58,59 Laboratory studies of interstellar analog ices have demonstrated the formation of enols – the thermodynamically less stable tautomers of aldehydes and ketones – in astrochemically relevant ice mixtures after the exposure of energetic electrons; these low temperature experiments detected vinyl alcohol (C 2 H 3 OH), 16,20 1-propenol (CH 3 CHCH(OH)), 20 2-hydroxyacrylic acid (CH 2 (COH)COOH), 37 ethynol (HCCOH), 60 1,2-ethenediol (HOCHCHOH) 45 and 1,1-ethenediol (H 2 CC(OH) 2 ), 61 suggesting that enols should be ubiquitous in the interstellar medium. 16,45,61 However, only vinyl alcohol 62 and 1,2-ethenediol 63 have been detected in deep space so far. In organic synthesis, simple enols are usually regarded as short-lived species, 64 however, in enzymatic mechanisms, they are long-lived species playing key roles as intermediates.…”

Formation of Thioformic Acid (HCOSH)─The Simplest Thioacid─in Interstellar Ice Analogues

“…24,25 Such molecules formed in the interstellar ices can be eventually incorporated into comets and may be delivered to planets such as Earth. 26 Therefore, our results further contribute to the understanding of the formation pathways of sulfur-bearing molecules detected in the ISM, shed light on the prebiotic synthesis of proteins, 14 and thus expand our knowledge on the evolution of biorelevant molecules in the universe.…”

“…Table S2 summarizes the IR absorption features of the pristine ice and new absorption features after irradiation. The formyl radical (HĊO) is identified from the ν 3 fundamental (CO stretch) at 1840 cm –1 in irradiated ices. , The feature at 2045 cm –1 was present prior to the irradiation and was assigned to the overtone mode (2ν 2 ) of hydrogen sulfide; however, this peak increased after irradiation, suggesting that it is also associated with the formed products. Ferrante et al reported the absorption features of OCS (ν 3 ) at 2047 and 2054 cm –1 in CO–OCS ice and CO 2 –OCS ice at 11 K, respectively .…”

“…Exploiting the advantages of vacuum ultraviolet (VUV) photoionization reflectron time-of-flight mass spectrometry (PI-ReToF-MS) in the present experiments, the subliming products in the irradiated ices were detected in the gas phase via fragment-free isomer-specific photoionization during the temperature-programmed desorption (TPD), as the irradiated ices are heated from 5 K to 320 K . The identification of thioformic acid ( 1 ) has important implications for the formation of prebiotic sulfur-bearing molecules, such as cysteine which may be a catalyst and precursor in the prebiotic synthesis of peptides. , Such molecules formed in the interstellar ices can be eventually incorporated into comets and may be delivered to planets such as Earth . Therefore, our results further contribute to the understanding of the formation pathways of sulfur-bearing molecules detected in the ISM, shed light on the prebiotic synthesis of proteins, and thus expand our knowledge on the evolution of biorelevant molecules in the universe.…”