|dc.description.abstract||N-Alkyl amides undergo photodecomposition much slower
than their ketone, ester, and aldehyde analogs . The Norrish
Type II process in amides is also less important than in
these other classes of compounds due to electronic and geometric
effects. Type II products account for less than 10%
of the decomposed amides in all cases and usually less than
A 2% solution of amide in dioxane, when irradiated
through quartz with light >200 nm, did not decompose in the
Type II fashion to yield N-alkyl acetamides, alkenes, and
unsubstituted amides. The preferred reaction mode was the
Norrish Type I process where the O=C+N bond or the O=C+C
bond was cleaved to yield either an acyl radical and amine
radical or an acyl radical and alkyl radical. These photochemically
unstable radicals, once produced, rapidly underwent
secondary reactions to yield smaller molecules. These
molecules were detected, underwent further reactions (polymerization;
photoreduction), or interacted with the solvent .
The dimers of dioxane and cyclohexane, created via hydrogen
abstraction, were the main products of amide photodecomposition in these solvents. Small aldehydes and alkenes
produced as intermediates, underwent inefficient photoreductions
with solvent to afford alkyl dioxanes and cyclohexanes
and the two diastereomers of ( 2-p-dioxyl ) ethanol
as other major products. The alcohols were also produced
by photoreduction of acetaldehyde and hexanal as well as
by direct photodecomposition of dioxane .
Tertiary amides reacted faster than secondary amides.
The Type I reaction was accelerated by electronic (inductive)
factors. The Type II reaction was also more efficient due
to geometric and electronic factors. The Type I amine product, dihexylamine, was observed as an intermediate in the
photodecomposition of N, N-dihexylhexanoamide .
Unsymmetrical anilide imides photodecomposed in dioxane
to yield a wide variety of products. The Photo-Fries decomposition
mode was most favored where acyl groups migrated to
positions ortho and para to the amine substituent. For example, N-acetyl-butyranilide decomposed to yield o- and p-acetoaniline, o - and p-butyraniline , o- and p-acetobutyranilide,
and o- and p-butyracetanilide. Very little Type II
decomposition was observed, that is, N-acetyl-butyranilide
yielding N, N -diacetylaniline or o- and p-acetoacetanilide.
N-Alkylphthalimides were the sole group of amides or
imides reported in the literature to undergo efficient Y-hydrogen
abstraction. These compounds underwent initial
Y-hydrogen abstraction to yield a 1,4-biradical followed by
ring closure to form an azacyclobutanol intermediate. The intermediate then underwent retrotransannular ring opening
to yield various 3,4-benzo-6,7-dihydro(1H)azepine-2,5-diones.
Dihydrophthalimide alkenes were minor products in acetonitrile
which arose after the initial y-hydrogen abstraction
via subsequent δ-hydrogen transfer.
Quantum yield determination as well as mechanistic
investigation was conducted . The quantum yields varied
from 0.023 to 0.003. Photolysis of an optically active
phthalimide with an asymmetric Y-position to yield starting
material of the same activity proved that the initial
hydrogen abstraction was irreversible. A Type I cleavage
to yield phthalic anhydride on treatment with silica gel
and heat was important when they Y-position was tertiary.
A quenching study of these N-alkylphthalimides with
piperylene showed acceleration of starting material disappearance
but decrease in product formation. An additional
reaction process was interfering with the azepinedione formation.
Liquid chromatography showed formation of several
highly alkylated products which could not be isolated in
N-Methylphthalimide, which could not ring expand, was
irradiated with various alkenes to produce analogous N-methylazepinediones. The mechanism involved a 2 + 2 cyclo-addition
of the double bond to the C-N bond to yield a dipolar
The intermediate with
a retrotransannular ring opening yielded the observed 3, 4-
benzo-6,7-dihydro-1-methylazepine-2,5-diones. These reactions prove that the C-N bond in phthalimide is of a substantial double bond character.||en_US