The Position of the Proton in Substituted Azobenzene Molecules

Klotz, Irving M.; Fiess, Harold A.; Ho, J.Y.; Mellody, Margaret

doi:10.1021/ja01649a041

Cited by 63 publications

(33 citation statements)

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“…These observations fail to lend support to the spectral interpretations suggested by Klotz et al 7 On the other hand the assignment of the 320 mp band, shown by 4dimethylaminoazobenzene in acidic solution, to the ammonium cation (Ib) is clearly reinforced . These observations fail to lend support to the spectral interpretations suggested by Klotz et al 7 On the other hand the assignment of the 320 mp band, shown by 4dimethylaminoazobenzene in acidic solution, to the ammonium cation (Ib) is clearly reinforced .…”

Section: Received October 26 1959contrasting

confidence: 73%

Notes- Bis(2-aminoethyl) Dithiolcarbonate Dihydrochloride: Intermediate in the Hydrolysis of 2-Thiazoline-2-thiol

Gaul¹,

Fremuth²

1960

J. Org. Chem.

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NOTES 869Ultraviolet spectra of disulfides. The ultraviolet spectra were obtained with the Beckman Recording Spectrophotometer, Model DK, using isooctane as a solvent. The curves are recorded in a thesis,' and the maxima: diphenyl disulfide, 241 (4.33), [A, (log e)] in m M are: 272 (3.57), 302 (3.26); his-(2,6-dimethylphenyl) disulfide, 225 (4.02), 260 (3.89), 305 (2.78); bis-(2,4,5-triisopropylphenyl) disulfide, 244 (4.18), 285 (3.56), 344 (284): bis-(2,4,6-triisopropylphenyl) disullide, 232 (4.18), 270 (4.07), 310 (3.51). All of the disulfides except diphenyl show a low order of absorption (log c ca. 0.2-0.4) at ea. 500-700 mp, which increases as the ultraviolet region is approached, and are pale yellow. The absorption spectrum of diphenyl disulfide checked well with that recorded.'*

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Section: Received October 26 1959contrasting

confidence: 73%

Notes- Bis(2-aminoethyl) Dithiolcarbonate Dihydrochloride: Intermediate in the Hydrolysis of 2-Thiazoline-2-thiol

Gaul¹,

Fremuth²

1960

J. Org. Chem.

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“…In aqueous sulfuric acid a pK, of -0.93 was reported by Klotz et al (5)' for ionization of the conjugate acid, corresponding to 50% protonation in about 20% H2S04. In aqueous sulfuric acid containing 20% ethanol a pK, of -1.02 was found by Yeh and Jaffk (6)3.…”

Section: -Hydroxyazobenzenementioning

confidence: 76%

“…The basic centre in the first protonation of 4-hydroxyazobenzene and related compounds is generally (5,17,18) taken to be the P-nitrogen, in accord with resonance stabilization of charge at that position:…”

Section: Discussionmentioning

confidence: 99%

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Diprotonation equilibria involving 4-hydroxyazobenzene and 4-hydroxyazobenzene-4′-sulfonic acid

Strachan¹,

Dolenko²,

Buncel³

1969

Can. J. Chem.

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4-Hydroxyazobenzene and 4-hydroxyazobenzene-4'-sulfonic acid, which are known to be protonated in dilute acid on the azo function, are shown through spectroscopic studies to undergo a second equilibrium protonation in the 100% H 2 S 0 4 region. The pKn2 values are -10.2 and -11.1 respectively. The spectral evidence suggests that with both substrates the second protonation occurs on the phenolic oxygen site, rather than on carbon.Canadian Journal of Chemistry, 47, 3631 (1969) The present work was undertaken as a preliminary to the study of the Wallach rearrangement of azoxybenzene in the 100% H 2 S 0 4 region. Extension of the hnetic and spectral studies (1,2) beyond 96% H2S04 was desirable for a number of reasons, one being the possibility that the postulated dicationic intermediate (3) might be stabilized in anhydrous acid. However, prior to such a kinetic-spectral study with azoxybenzene, it was required to have full understanding of the spectral behavior in such media of 4-hydroxyazobenzene, the normal product of rearrangement (4). The results recorded here reveal a rather complex pattern of spectral changes, which can be dissected into a second equilibrium protonation of 4-hydroxyazobenzene, a fairly rapid sulfonation process to give 4-hydroxyazobenzene-4'-sulfonic acid, as well as a second eauilibrium rot on at ion and the much slower sulfonation of this sulfonic acid derivative. Results 4-HydroxyazobenzeneThe protonation behavior of 4-hydroxyazobenzene in dilute acid has been examined previously (5,6). In aqueous sulfuric acid a pK, of -0.93 was reported by Klotz et al. (5)' for ionization of the conjugate acid, corresponding to 50% protonation in about 20% H2S04. In aqueous sulfuric acid containing 20% ethanol a pK, of -1.02 was found by Yeh and Jaffk (6)3.These data were confirmed in the present work using the medium4 5% dioxane-95% aqueous H2S04. For the neutral form A, , , was found to be 348 m p (E = 2.18 x lo4), while for the protonated form A, , , was 460 m p (E = 3.96 x lo4), with pK, -0.99 in this medium. Beyond 45% H2S04 (corresponding to about 99% protonation) no changes were observed in either A, , , or in&,,, until about 90 % H 2 S 0 2 , and the spectral absorption was also time invariant.4-Hydroxyazobenzene in 90-100% H2S04 has been observed to undergo further spectral changes which are time-dependent. In the region 90-96% H2S04 the initial A, , , is unchanged at 460 mp, but with time this absorption grows in intensity and simultaneously shifts to 465 mp. In the 96-100% H2S04 region, the initial absorption shifts gradually to shorter wavelengths until it reaches 426 mp. In these acidities the growth in peak height is more rapid: the product spectra exhibit a concurrent gradual shift to 450 mp. The above time-dependent spectral changes are shown to be the result of the conversion of 4-hydroxyazobenzene to the 4'-sulfonic acid and are dealt with in detail subsequently (see Experimental and reference 11). The immediate (zero time) spectral shifts are due to a protolytic equilibrium which was ...

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“…Protonation of the azo group results in a disruption of conjugation and consequently a change in color [24,25]. Methyl orange (1) is a common azobenzene dye that shows a sharp color change from orange to yellow around pH = 3.5 (pK a = 3.46), making it useful for the titration of weak acids.…”

Section: Applications and Examples (Environmental Changes)mentioning

confidence: 99%