Formic dimer

From computations with basis sets of the polarized 6-3IG type, at SCF and MP2 levels, the change from formic acid dimer to acetic acid dimer has only a very minor influence upon the energetics of binding . This conclusion is indeed verified by resonant laser photoacoustic spectroscopic measurements i 79,181,182 which find further that trifluoroacetic and propionic acid dimers have a very similar binding enthalpy to formic dimer. One may extrapolate that the formic acid dimer Fl-bond energy is probably applicable for most carboxylic acids with alkyl chains replacing the CH group. 

Two additional illustrations are given in Figures 6 and 7 which show fugacity coefficients for two binary systems along the vapor-liquid saturation curve at a total pressure of 1 atm. These results are based on the chemical theory of vapor-phase imperfection and on experimental vapor-liquid equilibrium data for the binary systems. In the system formic acid (1) - acetic acid (2), <() (for y = 1) is lower than formic acid at 100.5°C has a stronger tendency to dimerize than does acetic acid at 118.2°C. Since strong dimerization occurs between all three possible pairs, (fij and not... 

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carboiiyiation. Two types of the oxidative carbonyla-tion of alkynes are known. The first is a synthesis of the alkynic carbox-ylates 524 by oxidative carbonylation of terminal alkynes using PdCN and CuCh in the presence of a base[469], Dropwise addition of alkynes is recommended as a preparative-scale procedure of this reation in order to minimize the oxidative dimerization of alkynes as a competitive reaction[470]. Also efficient carbonylation of terminal alkynes using PdCU, CuCI and LiCi under CO-O2 (1 I) was reported[471]. The reaction has been applied to the synthesis of the carbapenem intermediate 525[472], The steroidal acetylenic ester 526 formed by this reaction undergoes the hydroarylalion of the triple bond (see Chapter 4, Section 1) with aryl iodide and formic acid to give the lactone 527(473],... 

The 2,3-alkadienyl acetate 851 reacts with terminal alkynes to give the 2-alkynyl-1,3-diene derivative 852 without using Cul and a base. In the absence of other reactants, the terminal alkyne 853 is formed by an unusual elimination as an intermediate, which reacts further with 851 to give the dimer 854. Hydrogenolysis of 851 with formic acid affords the 2, 4-diene 855[524]. 

Formic acid behaves differently. The expected octadienyl formate is not formed. The reaction of butadiene carried out in formic acid and triethylamine affords 1,7-octadiene (41) as the major product and 1,6-octadiene as a minor product[41-43], Formic acid is a hydride source. It is known that the Pd hydride formed from palladium formate attacks the substituted side of tt-allylpalladium to form the terminal alkene[44] (see Section 2.8). The reductive dimerization of isoprene in formic acid in the presence of Et3N using tri(i)-tolyl)phosphine at room temperature afforded a mixture of dimers in 87% yield, which contained 71% of the head-to-tail dimers 42a and 42b. The mixture was treated with concentrated HCl to give an easily separable chloro derivative 43. By this means, a- and d-citronellol (44 and 45) were pre-pared[45]. 

In the vapor phase formic acid forms a hydrogen-bonded dimer ... 

At room temperature and atmospheric pressure, 95% of the vapor consists of dimers (13). The properties of the vapor deviate considerably from ideal gas behavior because of the dimeri2ation. In the soHd state, formic acid forms infinite chains consisting of monomers linked by hydrogen bonds (14) ... 

The chain stmcture persists in Hquid formic acid, but in solution in hydrocarbons the dimeric form predominates (15). 

Tables 13-1, 13-2, and 13-4 include data on formic acid and acetic acid, two substances that tend to dimerize in the vapor phase according to the chemical-equilibrium expression...

A calculation of tunneling splitting in formic acid dimer has been undertaken by Makri and Miller [1989] for a model two-dimensional polynomial potential with antisymmetric coupling. The semiclassical approximation exploiting a version of the sudden approximation has given A = 0.9cm" while the numerically exact result is 1.8cm" Since this comparison was the main goal pursued by this model calculation, the asymmetry caused by the crystalline environment has not been taken into account. 

A similar behavior is found in the 1 2 inclusion of 26 with formic acid 71 (Fig. 20, type II). We notire a H-bonded dimer of 26 and one of the formic acid molecules binding the host dimer in a pseudo-dimeric arrangement via the free —COOH groups of the host dimer. The second guest molecule is also placed into an interstitial tunnel of the dimeric host/bound-guest matrix. Here the 1 2 stoichiometry is due to the small size of the guest partner. 

The structures of the acetic acidS0) and of the propionic acid71 inclusions of 26 (Fig. 20, type III) are isomorphous to each other. The increased guest volume with respect to formic acid yields 1 1 stoichiometry, with no H-bonds between host and guest molecules in either case. The tunnel where the dimers of guests are situated (see Fig. 32 a) is functionally the same as in the case of the self-dimerized pairs of the formic acid guests. 

Chojnacki, H., J. Andzelm, D. T. Nguyen, and A. Sokalski. 1995. Preliminary Density Functional Calculations on the Formic Acid Dimer. Computers and Chemistry 19,181. 

A different dimerization takes place in formic acid (33. 34). Unlike other carboxylic acids which behave as nucleophiles, formic acid behaves as a reductant and the dimerization proceeds with partial reduction. By carrying out the reaction in a mixture of formic acid and triethylamine at 59°C using Pd(OAc)2, 1,6-octadiene (24) was obtained. 

Heck tried the reductive dimerization of isoprene in formic acid in the presence of triethylamine at room temperature using 1% palladium phosphine catalysts to give dimers in up to 79% yield (95). Better selectivity to the head-to-tail dimer was obtained by using Pd(OAc)2 with 1 1 ratio of arylphosphines. THF as solvent showed a favorable effect. In a scaled-up reaction with 0.5 mole of isoprene using 7r-allylpalladium acetate and o-tolyphosphine, the isolated yield of the dimers was 87%. The dimers contained 71% of the head-to-tail isomers. The mixture was converted into easily separable products by treatment with concentrated hydro-... 

The mechanism of the reductive dimerization was studied by using both dideuterated and carboxyl-deuterated formic acid. The carboxyl deuterium was found on carbon 6, and the other deuterium on carbon 3 of 2,6-dimethyl-1,7-octadiene. 

In one mechanism, Pd° generated by reduction of Pd2+ with formic acid forms hydridoformatopalladium complex 102, which reacts with isoprene to form formato(methylbutenyl)palladium complex 103. Then, insertion of the second molecule of isoprene takes place. Finally, reductive elimination and evolution of carbon dioxide give the dimers ... 

Ammonium cerium(IV) nitrate on reaction with acetone or acetophenone generates acetyl- or benzoylformonitrile oxides, respectively (99). These nitrile oxides dimerize to furoxans and give, in the presence of alkenes and alkynes, 3-acetyl- or 3-benzoyl-4,5-dihydroisoxazoles and 3-acetyl- or 3-benzoylisoxazoles, respectively the yield of the isoxazole derivatives was improved on using ammonium cerium(III) nitrate tetrahydrate-formic acid (99). 

P. Zielke and M. A. Suhm, Raman jet spectroscopy of formic acid dimers Low frequency vibrational dynamics and beyond. Phys. Chem. Chem. Phys. 9, 4528 4534 (2007). 

G. V. Mil nikov, O. Kuhn, and H. Nakamura, Ground state and vibrationally assisted tunneling in the formic acid dimer. J. Chem. Phys. 123, 074308 (2005). 

Contrary to all other reactions with acids the behaviour of the zwitterion towards vapours of formic acid is intriguing, since no proton transfer is observed. The formic acid vapour uptake generates a material composed of pairs of zwitterion molecules, linked by O-H- - O bonds between the protonated -COOH and the deprotonated -COO() groups [0---0 separation 2.526(4) A] residing on the organometallic moiety. The zwitterion dimers interact with two formic acid molecules via 0-H---0 and C-H---0 hydrogen bonds [0---0 distance 2.541(4),... 

The stability of the uracil dimer is the subject of conflicting reports. Ishihara reports33 that it is destroyed by IN NaOH at 100°C, and Wacker states that it is unstable in acid, alkali, or even in boiling water. Setlow et al.46 report that 50% of the uracil dimer is destroyed by formic acid hydrolysis (presumably at 175°C). But Smith32 found it to be stable to boiling water, IN NH4OH, IN HC1, and trifluoracetic acid both at room temperature and at 155°C. 

Oxidative cyclizations of cyclodipeptides incorporating tryptophan have also been reported (81TL5323). Thus, irradiation of the piperazinedione (39) in formic acid in the presence of a sensitizer such as proflavine or chloranil gave the hydroxypyrroloindole (40). Oxidation with thallium (III) trifluoroacetate gave the dimer (41) in 3% yield. 

Nitrosyl formate may be generated in situ by treating isopentyl nitrite with anhydrous formic acid. This reagent evidently adds to olefins such as cyclohexene, styrene, norbomene, trans-3-hexene, and 2,3-dimethylbutene to give nitrosoformates. While the first three olefins were converted into dimeric products, 2,3-dimethylbutene produced a 50-50 mixture of the monomer and the dimer (as a blue oil). The product of the reaction with trans-3-hexene contained some of the corresponding oximino formate. 

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