Oxidation of a Water-Soluble Phosphine and Some Spectroscopic Probes with Nitric Oxide and Nitrous Acid in Aqueous Solutions

Abstract

In acidic aqueous solutions, nitrogen monoxide oxidizes monosulfonated triphenylphosphine, TPPMS(-), to the corresponding phosphine oxide. The NO-derived product is N(2)O. This chemistry parallels that reported for the reaction of NO with the unsubstituted triphenylphosphine in nonpolar organic solvents, but the rate constant measured in this work, 5.14 x 10(6) M(-2) s(-1), is greater by several orders of magnitude. This makes TPPMS(-) a useful analytical reagent for NO in aqueous solution. The increased rate constant in the present work appears to be a medium effect, and unrelated to the introduction of a single sulfonate group in the phosphine. The reaction between nitrous acid and TPPMS(-) has a 2:1 [TPPMS(-)]/[HNO(2)] stoichiometry and generates NH(2)OH quantitatively. The rate law, rate = 4k(d)[HNO(2)](2)[TPPMS(-)], identifies the second-order self-reaction of HNO(2) as the rate-limiting step that generates the active oxidant(s) for the fast subsequent reaction with TPPMS(-). It appears that the active oxidant is N(2)O(3), although the oxides NO and NO(2) derived from it may be also involved. Bimolecular self-reaction of HNO(2) also precedes the oxidations of ABTS(2-) and TMPD. Competing with this path are the acid-catalyzed oxidations of both reagents via NO(+).

Capture of NO by a Frustrated Lewis Pair: A New Type of Persistent N‐Oxyl Radical

“…The NÀO bond distance in 3 of 1.2962(17) is significantly lengthened relative to that of free NO (1.151 ); [12] it is similar to that found in N-oxyl radicals R 2 N-OC such as TEMPO (4: 1.284(8) ) [13] and tBu 2 N-OC (1.28(2) (gas phase) [14] ). The odd-electron species 3 exhibits an X-band EPR signal at room temperature in fluorobenzene solution consistent with coupling of the electron spin to the 14 N nucleus as well as to 31 P and 11/10 B nuclei ( Figure 2). Simulation of the symmetric pattern about g = 2.0089 gives A( 14 N) = 18.5 MHz, A( 31 P) = 48.5 MHz, and A( 11 B) = 9.1 MHz (contribution from 10 B neglected).…”

“…[7] Without such mechanistic ambiguity, 3 also undergoes HAA with the significantly stronger CÀH bonds of ethylbenzene (C-H BDE % 85 kcal mol À1 ) [19] following clean pseudo first-order kinetics in 3 employing excess ethylbenzene substrate (4-7 m) in fluorobenzene to give k ethylbenzene (25 8C) = 5.6(3) 10 À6 m À1 s À1 . The reaction of 3 with excess ethylbenzene gives a 1:1 ratio of 7 along with the new Ofunctionalized product P/B-FLP-NO(1-CH(Me)Ph) (9; Scheme 2) as monitored by 31 …”

“…For instance, modulation of FLP-NO-H and FLP-NO-R bond strengths may lead to selective radical addition and/or HAA reactions. Moreover, a decrease in the strength of the FLP-NO interaction could lead to the reversible binding of NO as well as provide insight into phosphine-based approaches to sense and quantify NO [31] and HNO. [32] Our study expands frustrated Lewis pair chemistry to radical species providing access to unprecedented areas of chemistry by the cooperative action of pairs of potent Lewis bases and acids sterically prevented from achieving a strong donor-acceptor interaction in the absence of a mediating molecule.…”

Frustrated Lewis pair chemistry of carbon, nitrogen and sulfur oxides

“…In contrast, phosphines typically react with NO following a third-order rate law, rst order in phosphine and second order in NO to generate N 2 O and phosphine oxide. [88][89][90] This latter reactivity is also seen for the reaction of the intermolecular FLP 1 with NO, affording t Bu 3 PO and N 2 O. 58 The latter product was trapped in as the species t Bu 3 P(N 2 O)B(C 6 F 5 ) 3 (108) which was described above.…”

“…31 The reactions affording CO 2 reduction are thus thought to proceed through a dissociative process in which solventinduced dissociation of AlX [(C 6 F 5 )CO 2 Al(C 6 F 5 ) 2 ] 2 (88) are produced (Scheme 19). While 87 was not isolable, the analog (otol) 3 PCO 2 Al(OC(CF 3 ) 3 ) 3 (89) was prepared and fully characterized. 31 These data support a mechanism in which a series of dissociative equilibria generate AlX 3 , the analog of 2, and free phosphine permitting an associative insertion reaction of CO 2 with [Al 2 X 6 ] (Scheme 19).…”