494
B. A. Howell, K. E. Carter
heat feedback from the flame and pyrolytic decomposition
of the polymer to generate volatile fuel fragments to feed
the flame. These materials are most effective in oxygen-
containing polymers. For flame-retarding polymers lacking
oxygen in the structure, an oxygen rich promoter (pentae-
rythritol, dipentaerythritol, etc.) may be used in conjunc-
tion with the organophosphorus compound. It is thought
that during combustion, phosphoric acid is generated which
promotes crosslinking of the polymer and char formation.
Recently, some remarkably effective gas-phase active
organophosphorus flame retardants have been developed to
replace tetrabromobisphenol A in the production of epoxy
resins. Much of this is based on the incorporation of 9,10-
dihydro-9-oxa-10-phosphaphenathrene 10-oxide (DOPO)
into either the epoxy component or the hardener [15–21].
During polymer pyrolysis, these compounds extrude PO
radical to the gas phase where it may function as an effi-
cient scavenger of flame-propagating radicals. As a con-
sequence, adequate flame retardance can be achieved at
very low loading of these materials in the polymer matrix.
Tartaric acid, 2,3-dihydroxybutanedioic acid, is a prin-
cipal by-product of the conversion of grape stock to wine
by fermentation [22, 23]. This compound has a storied
history. Crystals of a salt, potassium ammonium tartrate,
were the object of the first resolution (by manual means) of
a racemic mixture by Pasteur. This demonstrated the
existence of enantiomeric compounds. Pasteur’s interest in
the formation of this compound led to the demonstration
that the presence of yeast or bacteria is required for fer-
mentation, i.e., that enzymes are required for the conver-
sion of carbohydrates, primarily glucose and other simple
monosaccharides, to ethanol. He also was able to demon-
strate that spoilage due to bacterial contamination could be
avoided by heating the medium to 52–60 °C for a short
time, a process now known as pasteurization and which has
been immensely useful for preservation by the food
industry.
on the walls and bottoms of wine storage tanks [27–30].
Cream of tartar also crystallizes in tanks of filtered wine
undergoing refrigeration [30].
Tartaric acid may be readily converted to the corre-
sponding diethyl ester [31, 32]. This compound represents
a useful starting point for the synthesis of ‘‘green’’ flame-
retardant materials based on a plentiful, inexpensive, and
renewable by-product of the thriving Michigan wine
industry.
Experimental
General
In general, reactions were carried out in a dry (all glassware
was dried in a oven overnight at 120 °C and allowed to cool
under a stream of dry nitrogen prior to use) three-necked,
round-bottomed flask fitted with Liebig condenser bearing a
gas-inlet tube, a magnetic stirring bar (or Trubore stirrer),
and a pressure-equalizing dropping funnel (or syringe port).
Chromatography was accomplished using SilaFlash P60
(230–400 mesh silica; Silicycle) in a column of appropriate
size and hexane/ethyl acetate as eluant. Silica-coated Mylar
plates (ThermoFisher Scientific) were used for thin layer
chromatography (TLC). Melting points were determined by
differential scanning calorimetry (DSC) using TA Instru-
ments 2910 MDSC. All samples were analyzed at a heating
rate of 5 °C min-1 in a constant nitrogen purge of 50 cm3
min-1. Thermal decomposition temperatures were obtained
using a TA Instruments 2950 Hi-Res TGA instrument
interfaced with the Thermal Analyst 2100 control unit.
Most generally, a heating rate of 5 °C min-1 was used. TA
Thermal Advantage software was used for data analysis.
Samples (5–10 mg) were contained in a platinum pan.
The sample compartment was purged with dry nitrogen
at 50 cm3 min-1 during analysis. Nuclear magnetic reso-
nance (NMR) spectra were obtained using a 10 to 25%
solution in deuterochloroform or dimethyl sulfoxide-d6 and
a Varian Mercury 300 MHz spectrometer. Proton and car-
bon chemical shifts are reported in parts-per-million (d)
with respect to tetramethylsilane (TMS) as internal refer-
ence (d = 0.00). Phosphorus chemical shifts are in d with
respect to 85% aqueous phosphoric acid solution as external
reference (d = 0.00). Infrared (IR) spectra were obtained
using thin films between sodium chloride plates or solid
solutions (1%) in anhydrous potassium bromide (as discs)
and a Nicolet MAGNA-IR 560 spectrometer. Absorptions
were recorded in wave numbers (cm-1), and absorption
intensities were classified in the usual fashion as very weak
(vw), weak (w), and medium (m), strong (s), and very strong
(vs) relative to the strongest band in the spectrum. Mass
spectra were obtained using a Hewlett-Packard 5890A gas
The United States ranks fourth behind Italy, France, and
Spain in wine production accounting for about 10% of
the total. Wine is widely produced in the United States
but large-volume production is localized in a few regions
[24, 25]. Michigan ranks fourth among the US states in
acreage devoted to grape growing and thirteenth in the
production of wine [26]. Vineyards are located in south-
west Michigan near Fennville and in the peninsular region
near Traverse City. All are located within 25 miles of the
Lake Michigan shore. The lake effect provides a favorable
microclimate for grape production. The presence of this
robust wine industry provides an annual, renewable source
of tartaric acid. Tartrates occur naturally in winery pomace,
in still slops from brandy distillation, in lees that settle in
wine tanks, and in argols that separate as a crystalline
coating of nearly pure cream of tartar (potassium bitartrate)
123