The invention is related to compounds, being useful in treating psychosis, of the formula: ##STR1## wherein R.sup.1 is lower-alkyl, or phenyl-lower-alkyl; R.sup.2, R.sup.3 and R.sup.4 are the same or different lower-alkyl; n is zero or one; R.sup.5 is hydrogen, lower-alkyl, C.sub.3 -C.sub.7 -monocyclic cycloalkyl, lower-alkoxy, phenyl, phenyl-lower-alkyl, phenyl-lower-alkyl in which the phenyl ring is substituted in the 2, 3, or 4-position by one to two, the same or different, halogen substituents, or R.sup.5 is a 5-membered aromatic monocyclic heterocycle selected from the group consisting of thienyl, furanyl and isoxazolyl; R.sup.6 is hydrogen or lower-alkyl; or when n is zero, R.sup.5 and R.sup.6 together are --(CH.sub.2).sub.m -- wherein m is an integer from four to six; with the proviso that when R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are methyl, n is zero and R.sup.6 is hydrogen or methyl, R.sup.5 cannot be hydrogen; further provided that when n is zero, R.sup.5 cannot be lower-alkoxy, phenyl, or a 5-membered aromatic monocyclic heterocycle, or a pharmaceutically acceptable acid-addition salt thereof.

Acidic gases containing carbon dioxide are removed from a normally gaseous mixture by absorbing CO.sub.2 from the gaseous mixture with an aqueous solution comprising a basic alkali metal salt or hydroxide and an activator or promoter system for the salt or hydroxide which contains (i) at least one non-sterically hindered diamine defined as having both a primary and a tertiary amino moiety wherein the primary amino moiety is attached to a primary carbon atom, and (ii) an amino acid, and desorbing at least partially the absorbed CO.sub.2 from the aqueous solution.