Transparent soap bar process using trialkylamine oxide dihydrate

Transparent soap bars are made by a process comprising mixing solid, non-hydroscopic trialkylamine oxide dihydrate with a fatty acid soap and other conventional ingredients such as triethanolamine, glycerine, water, perfume, and the like.

BACKGROUND 
Transparent soap bars have been on the market for many years. They are 
considered aesthetically pleasing to the eye. They are generally defined 
as having sufficient transparency so that fourteen point type can be read 
through a one-quarter inch thick bar. When properly formulated, they are 
quite mild but are somewhat deficient in hard water properties. 
Furthermore, they are fairly soft due to their water content and have poor 
slough properties. Typical transparent soap bars are described in Kamen 
U.S. Pat. No. 3,562,167, Jungermann et al. U.S. Pat. No. 4,758,370, and 
Poper et al. U.S. Pat. No. 4,290,904, which are incorporated herein by 
reference. 
It has been suggested to use alkyl dimethylamine oxides in transparent 
detergent bars because of their excellent foaming properties (cf. Poper et 
al. U.S. Pat. No. 4,290,904). However, a satisfactory way of doing this on 
a commercial scale has not been developed. The problem is that alkyl 
dimethylamine oxides (e.g., dodecyl dimethylamine oxide) are made by 
reacting aqueous hydrogen peroxide to form an aqueous solution of the 
alkyl dimethylamine oxide. In practice it has been reported that such 
solutions should not exceed about 30 weight percent active alkyl 
dimethylamine oxides or the solution will form an unstirrable gel 
preventing completion of this reaction. Commercially lauryl dimethylamine 
oxide is sold as a 30 weight percent aqueous solution. Use of this 30 
weight percent solution of alkyl dimethylamine oxide in formulating a soap 
bar leads to the introduction of an excessive amount of water into the 
soap bar. For example, if this bar is formulated to contain 10 weight 
percent alkyl dimethylamine oxide, it will of necessity contain at least 
23.3 weight percent water. Such high water levels lead to a very soft soap 
bar with an unacceptable slough rate. On the laboratory scale this problem 
appears to have been circumvented by distilling this water from the alkyl 
dimethylamine oxide solution to form an anhydrous alkyldimethylamine oxide 
which can be used in the laboratory preparation of a soap bar as shown in 
Poper et al. U. S. Pat. No. 4,290,904. However, it is impractical to 
convert 30 weight percent aqueous solutions of alkyl dimethylamine oxides 
to a dry product on a commercial scale because of the large amount of 
water involved. Hence, a need exists for an efficient method of making 
transparent soap bars which contain an effective amount of alkyl 
dimethylamine oxide without introducing an excessive amount of water and 
without the need to perform the arduous removal of water from the 
commercial alkyldimethylamine oxide solution. 
SUMMARY 
According to the present invention, transparent soap bars which contain 
effective amounts of alkyl dimethylamine oxides and which possess 
excellent slough characteristics can be made by mixing a non-hygroscopic 
alkyl dimethylamine oxide dihydrate with a fatty acid soap and other 
ingredients conventionally used in transparent soap bars.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of this invention is a method of making a 
transparent soap bar, said method comprising mixing (i) a non-hygroscopic 
trialkylamine oxide dihydrate having the structure: 
EQU R'R"R"'NO.multidot.2H.sub.2 O 
wherein R' is a primary alkyl containing 8-24 carbon atoms, R" is methyl, 
ethyl or a primary alkyl containing 8-24 carbon atoms and R"' is methyl or 
ethyl, and (ii) a fatty acid soap and optionally other conventional 
transparent soap bar ingredients, the amount of said trialkylamine oxide 
dihydrate being sufficient to comprise 1-25 weight percent of the 
resultant transparent soap bar. 
The essential trialkylamine oxide dihydrates can be made by the process 
described in Application Ser. No. 344,275, filed Apr. 26, 1989. According 
to this process, the appropriate amine is reacted with at least a 
stoichiometric amount of concentrated (e.g., 50-70 weight percent active) 
hydrogen peroxide in an organic ester solvent (e.g., ethyl acetate) in an 
amount sufficient to maintain a fluid reaction mixture. Reaction 
temperatures of about 25-100.degree. C. can be used. A preferred range is 
60-75.degree. C. Carbon dioxide can be injected to promote the reaction. 
Use of about 1.2 theories of 70 weight percent hydrogen peroxide results 
in a final reaction mixture which contains about 2 moles of water per mole 
of amine oxide. If more water than this is present, it should be distilled 
out to obtain a 2/1 water/amine oxide mole ratio. The organic ester 
solution can then be cooled causing the amine oxide dihydrate to 
crystallize. Alternatively, the organic ester can be distilled out at 
atmospheric pressure or under vacuum to obtain the amine oxide dihydrate 
as the residue. It was surprisingly found that the tert-amine oxide 
dihydrate was not hygroscopic. 
Trialkylamines useful in making the tert-amine oxide dihydrate are those 
having the formula R'R"R"'N wherein R', R" and R"' are as previously 
defined. Representative examples of these are: 
n-octyl diethylamine 
n-decyl dimethylamine 
n-decyl diethylamine 
n-dodecyl dimethylamine 
n-dodecyl diethylamine 
n-tetradecyl dimethylamine 
n-hexadecyl diethylamine 
n-octadecyl dimethylamine 
n-eicosyl dimethylamine 
di-(n-octyl)methylamine 
di-(n-decyl)methylamine 
di-(n-dodecyl)ethylamine 
di-(n-tetradecyl)methylamine 
di-(n-hexadecyl)ethylamine 
di-(n-octadecyl)methylamine 
di-(n-eicosyl)methylamine 
n-octyl n-dodecyl methylamine 
n-decyl n-octadecyl ethylamine 
n-decyl n-eicosyl ethylamine 
and the like including mixtures thereof. 
Of the above, a still more preferred class of tertamines consists of those 
in which R' is a C.sub.8-24 primary alkyl, R" is methyl or a C.sub.8-24 
primary alkyl and R"' is methyl. Examples of these are: 
octyl dimethylamine 
decyl dimethylamine 
dodecyl dimethylamine 
tetradecyl dimethylamine 
hexadecyl dimethylamine 
eicosyl dimethylamine 
docosyl dimethylamine 
tetracosyl dimethylamine 
dioctyl methylamine 
didecyl methylamine 
didodecyl methylamine 
decyl dodecyl methylamine 
ditetradecyl methylamine 
tetradecyl octyl methylamine 
and the like including mixtures thereof. 
The following Examples show how to make the required trialkylamine oxide 
dihydrate. 
EXAMPLE 1 
In a 250 milliliter glass reaction flask was placed 100 grams of 
tetradecyldimethylamine (0.41 mole; amine value 230.0 mg KOH/g amine) and 
0.5 gram (1.27 mmol) of diethylenetriaminepentaacetic acid. This was 
heated with stirring to 65 C and then 23 grams (0.47 mole) of 70 weight 
percent aqueous hydrogen peroxide was added dropwise over a 15-minute 
period. The mixture was then heated to 76.degree. C. and stirred at that 
temperature for seven hours. As needed, ethyl acetate (34 mL) was added 
dropwise to the reaction mass in order to maintain a clear, gel-free 
liquid. Analysis of the crude reaction mass showed 99 percent amine 
conversion by proton NMR. The crude reaction mass was added to 400 mL 
additional ethyl acetate. The solution was then cooled to 15.degree. C. 
forming a non-hydroscopic white crystalline solid tetradecyldimethylamine 
oxide dihydrate in 86% recovered yield melting at about 41.degree. C. 
EXAMPLE 2 
In a glass reaction flask was placed 100 g tetradecyl dimethylamine and 0.5 
g diethylenetriamine pentaacetic acid. Carbon dioxide sparge into the 
liquid phase was started and the mixture was stirred and heated to 
65.degree. C. The CO.sub.2 sparge was stopped and a CO.sub.2 gas phase was 
maintained over the reaction mixture. Dropwise feed of 70 weight percent 
aqueous hydrogen peroxide was started. At the same time, addition of ethyl 
acetate was commenced. After 10 minutes all the hydrogen peroxide and 28 
mL of ethyl acetate had been added. Cooling was required to maintain the 
temperature under 75.degree. C. Heat was applied and the reaction 
continued for two more hours. Dropwise addition of ethyl acetate was 
continued for the first 19 minutes of the two-hour period. Total ethyl 
acetate feed was 43 mL. The reaction mixture was a clear gel-free 
solution. The reaction mixture was analyzed by NMR showing a 100 percent 
amine conversion. The reaction mixture was poured into a flask containing 
400 mL of ethyl acetate and cooled to 15 C. Needle-like crystals of 
tetradecyl dimethylamine oxide dihydrate form (106 g) indicating a 87 
percent yield. 
The amount of the trialkylamine oxide dihydrate in the transparent bar can 
vary from about 1-25 weight percent. A preferred amount is about 3-15 
weight percent and most preferably 5-10 weight percent. 
Other ingredients in the transparent bar include at least one fatty acid 
soap. These include the sodium and/or amine salts of C.sub.12 -C.sub.20 
fatty acids, especially stearic ricinoleic acid, coco fatty acid, tallow 
fatty acid mixtures, and oleic acid. Suitable amines include ethanol 
amine, diethanol amine, and triethanol amine. The amount of fatty acid 
soap ranges from about 50-90 weight percent. 
Other conventional surfactants can optionally be included in these 
formulations but are not essential. These include sodium laurylsulfates, 
triethanolamine laurylsulfate, lauroyl sarcosine, nonylphenol ethoxylate 
(9). 
Glycerol is co-produced in the saponification of tallow and is generally 
included as a minor component, up to about 25 weight percent, in the 
formulated bar. Likewise, other polyols such are ethylene glycol, 
propylene glycol, polyethylene glycol. 
In the past it has not been practical to include trialkylamine oxides in 
toilet detergent bar formulations because such trialkylamine oxides are 
made in an aqueous solution to avoid gel formation. Solutions containing 
in excess of about 30 weight percent C.sub.8-24 alkyl dimethylamine oxide 
tend to gel. This prevents stirring of the reaction mixture. Use of the 
commercially available 30 percent alkyl dimethylamine oxide aqueous 
solutions in the process of making detergent bars introduces an excessive 
amount of water forming an unacceptably soft bar. The only way around this 
problem in the past appears to have been to distill out all the water from 
the trialkylamine oxide solution forming an anhydrous trialkylamine oxide. 
This is only useful on the laboratory scale. 
In the process of the present invention, the detergent bar is made by 
mixing a defined trialkylamine oxide dihydrate with the other components 
used to formulate the detergent bar. The lower carbon number dihydrates 
are liquids. For example, octyl dimethylamine oxide dihydrate melts at 
about I5.degree. C. The more preferred C.sub.12-24 alkyl dimethylamine 
oxide dihydrates are initially solids when made. For example, 
dodecyldimethylamine oxide dihydrate melts at about 30 C and 
octadecyldimethylamine oxide dihydrate melts at about 62.degree. C. They 
may be produced in flaked, crystalline or drum cast form. The flaked and 
crystalline material may be readily added to the mixing vessel as a solid. 
If it is preferred to handle liquid materials the dihydrates may be heated 
to form a molten product and added to the mixing unit as a liquid. Such 
trialkylamine oxide dihydrates have been found to be non-hygroscopic and 
can be readily mixed with other components used to make a useful detergent 
bar without introducing an excessive amount of water. The trialkylamine 
oxide dihydrates can be made by the process described in our earlier U. S. 
Patent Application Ser. No. 344,275, filed Apr. 26, 1989, now abandoned. 
The present method of making a transparent detergent bar is shown in the 
following Example. 
EXAMPLE 3 
In a mixing vessel was placed 5.5 pph (parts by weight per 100 parts final 
blend) crystalline n-tetradecyl dimethylamine oxide dihydrate, 34 pph of 
sodium salt of a 80/20 mixture of tallow and coco fatty acids, 34. pph 
triethanolamine, 10 pph stearic acid and 16.5 pph water. The mixture was 
warmed to about 70-80.degree. C. and the molten mixture stirred until 
homogeneous. It was then poured into soap bar molds and cooled to form 
clear, transparent light yellow sap bars. The bar had a pH of 9 in water. 
The soap bar was subjected to an industry-standard foam test. In this test, 
30 mL of a 0.1 weight percent aqueous solution of the test soap bar is 
placed in a 100 mL graduate. The graduate is stoppered and rotated 
end-over-end ten times. The initial foam volume (referred to as "flash 
foam") is measured. The foam is measured a second time after 5 minutes as 
an indication of foam stability. The test detergent bar made by the 
present process had a flash foam of 7 mL and a 5-minute foam of 6 mL in 
soft water. In hard water (2000 ppm as CaCO.sub.3) the flash foam was 5 mL 
and the 5-minute foam was 2 mL. Washing with the bar made by the present 
process left a smooth and moist skin feel.