1. A process for the preparation of an organic acid salt of a cationic surfactant derived from the condensation of a fatty acid with an esterified dibasic amino acid comprising the steps of:
(a) providing a reaction mixture comprising a mineral acid salt of the cationic surfactant and an alkali or alkaline earth metal salt of the organic acid;
(b) allowing the reaction between the mineral acid salt of the cationic surfactant and the alkali andor alkaline earth metal salt of the organic acid salt to proceed until substantially all of the mineral acid salt of the cationic surfactant has been converted to the organic acid salt of the cationic surfactant; and
(c) recovering the organic acid salt of the cationic surfactant from the reaction mixture.
2. The process of claim 1 wherein the cationic surfactant comprises an N\u03b1-(C1-C22) alkanoyl di-basic amino acid (C1-C22) alkyl ester.
3. The process of claim 2 wherein the cationic surfactant comprises an ester selected from the group consisting of N\u03b1-lauroyl-L-arginine ethyl ester, N\u03b1-lauroyl-L-histidine ethyl ester and N\u03b1-lauroyl-L-tryptophan ethyl ester.
4. The process of claim 3 wherein the cationic surfactant comprises N\u03b1-lauroyl-L-arginine ethyl ester.
5. The process of claim 1 wherein the mineral acid salt is selected from the group consisting of the hydrochloride, hydrobromide, nitrate, nitrite, phosphate, phosphite and sulfate.
6. The process of claim 1 wherein the alkali or alkaline earth metal salt of the organic acid is employed in a molar amount of about 1 to about 1.5 moles per mole of the mineral acid salt.
7. The process of claim 1 wherein the alkali metal comprises sodium.
8. The process of claim 1 wherein step (b) is carried out at a temperature in the range of about 20 to about 100\xb0 C. for a period of time of about 0.5 to about 10 hours.
9. The process of claim 1 wherein step (a) is carried out in the absence of any diluent and the mineral acid salt is present in the reaction mixture in a molten state.
10. The process of claim 1 wherein a diluent is present in the reaction mixture.
11. The process of claim 10 wherein the mineral acid salt and the diluent are present in the reaction mixture in a ratio of about 2 to about 10 wv, based on the weight of the mineral acid salt.
12. The process of claim 10 wherein the diluent comprises water.
13. The process of claim 10 wherein the diluent has a Hildebrand Solubility Parameter in the range of about 7 to about 17.
14. The process of claim 10 wherein the diluent is selected from the group consisting of C1-C4 straight chain alcohols, C1-C4 branched chain alcohols, C1-C4 straight chain esters of C1-C8 monobasic organic acids, branched chain esters of C1-C8 monobasic organic acids, C3 and higher glycols, C3 and higher glycol ethers, C3 and higher hydroxy alcohols, C3 and higher ketones, C4 and higher hydroxy ketones, C4 and higher aliphatic ethers, C4 and higher cyclic ethers, C5 and higher straight chain alkanes, C5 and higher branched chain alkanes, C5 and higher cyclic alkanes and mixtures thereof.
15. The process of claim 14 wherein the diluent comprises an alcohol selected from the group consisting of ethanol, n-propanol, isopropanol and n-butanol.
16. The process of claim 13 wherein the diluent comprises an ester selected from the group consisting of ethyl acetate, methyl acetate, n-butyl acetate and ethyl formate.
17. The process of claim 13 wherein the diluent is selected from the group consisting of ethyl acetate and propylene glycol.
18. The process of claim 1 wherein the organic acid is selected from the group consisting of acetic acid, benzoic acid, butyric acid, capric acid, caproic acid, caprylic acid, citric acid, formic acid, fumaric acid, gluconic acid, glyceric acid, glycolic acid, heptanoic acid, lactic acid, lauric acid, linoleic acid, maleic acid, malic acid, myristic acid, nonanoic acid, oleic acid, palmitic acid, propionic acid, salicyclic acid, sorbic acid, stearic acid, tartaric acid, undacanoic acid, undecylenic acid and valeric acid.
19. The process of claim 16 wherein the organic acid is selected from the group consisting of acetic acid, citric acid, lactic acid and lauric acid.
20. The process of claim 17 wherein the organic acid comprises acetic acid.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An apparatus comprising:
a resistive divider circuit, comprising a first resistor and a second resistor;
a modulated resistor circuit, operatively coupled to the resistive divider circuit, wherein the second resistor and the modulated resistor circuit form an effective resistor circuit providing an effective attenuation; and
a variable duty cycle generator, to generate a variable duty cycle signal, wherein the variable duty cycle signal modulates the modulated resistor circuit to control the effective attenuation until an output of a differential circuit is within a predetermined range.
2. The apparatus of claim 1, wherein the variable duty cycle generator is a delta-sigma modulator circuit.
3. The apparatus of claim 1, further comprising:
a differential circuit, wherein the resistive divider circuit is operatively coupled to an input of the differential circuit.
4. The apparatus of claim 3, wherein the differential circuit comprises a delta-sigma converter circuit.
5. The apparatus of claim 3, further comprising:
an input of the resistive divider circuit, wherein a voltage received at the input is attenuated to an operational voltage of the differential circuit.
6. The apparatus of claim 3, further comprising:
a second resistive divider circuit, comprising a third resistor and a fourth resistor;
a second modulated resistor circuit, operatively coupled to the resistive divider circuit, wherein the fourth resistor and the second modulated resistor circuit form a second effective resistor circuit providing a second effective attenuation; and
a second variable duty cycle signal, generated by the variable duty cycle generator, wherein the second variable duty cycle signal modulates the second modulated resistor circuit to control the second effective attenuation.
7. The apparatus of claim 6, wherein the second variable duty cycle signal is a complementary waveform of the variable duty cycle signal.
8. The apparatus of claim 1, wherein the modulated resistor circuit comprises:
a modulated resistor; and
a switch, coupled to the modulated resistor, the switch configured to receive the variable duty cycle signal from the variable duty cycle generator and modulate the modulated resistor.
9. The apparatus of claim 8, wherein the switch is configured to switch between a higher attenuation and a lower attenuation.
10. The apparatus of claim 8, wherein the switch is configured to open and to close the modulated resistor circuit.
11. The apparatus of claim 8, wherein the switch comprises one or more field-effect transistors.
12. The apparatus of claim 8, wherein the switch comprises a buffer switch circuit, configured to receive the variable duty cycle signal from the variable duty cycle generator.
13. A method comprising:
receiving a first signal as an input to a resistive divider circuit, the resistive divider circuit comprising a first resistor and second resistor;
receiving a variable duty cycle signal at a modulated resistor circuit, wherein the modulated resistor circuit is operatively coupled to the resistive divider circuit;
modulating the modulated resistor circuit, based on the variable duty cycle signal, wherein the modulated resistor circuit and the second resistor are configured to form an effective resistor circuit providing an effective attenuation; and
attenuating the first signal, wherein the effective resistor circuit controls the attenuation of the first signal.
14. The method of claim 13, wherein the variable duty cycle signal is received from a delta-sigma modulator circuit.
15. The method of claim 13, further comprising:
supplying the attenuated first signal to an input of a differential circuit.
16. The method of claim 15, wherein the differential circuit comprises a delta-sigma converter circuit.
17. The method of claim 15, further comprising:
receiving a second signal as an input to a second resistive divider circuit, the second resistive divider circuit comprising a third resistor and fourth resistor;
receiving a second variable duty cycle signal at a second modulated resistor circuit, wherein the second modulated resistor circuit is operatively coupled to the second resistive divider circuit;
modulating the second modulated resistor circuit, based on the second variable duty cycle signal, wherein the second modulated resistor circuit and the fourth resistor are configured to form a second effective resistor circuit providing a second effective attenuation;
attenuating the second signal, wherein the second effective resistor circuit controls the attenuation of the second signal; and
supplying the attenuated second signal to a second input of the differential circuit.
18. A method comprising:
receiving a common mode signal at an input of a resistive attenuator network, wherein the resistive attenuator network is operatively coupled to the inputs of a differential circuit; and
adjusting an attenuation of the resistive attenuator network, based on varying a duty cycle of a signal, until an output of the differential circuit reaches a value approximating zero.
19. The method of claim 18, further comprising:
varying the duty cycle signal using a line equation.
20. The method of claim 19, further comprising:
calculating a gradient and an intercept of the line equation using the duty cycle of the signal and the output of the differential circuit as variables.
21. The method of claim 18, further comprising:
setting the duty cycle of the signal.