  We represent sixteen-component values "sedeons", generating associative
noncommutative space-time algebra. We demonstrate a generalization of
relativistic quantum mechanics using sedeonic wave functions and sedeonic
space-time operators. It is shown that the sedeonic second-order equation for
the sedeonic wave function, obtained from the Einstein relation for energy and
momentum, describes particles with spin 1/2. We show that for the special types
of wave functions the sedeonic second-order equation can be reduced to the set
of sedeonic first-order equations analogous to the Dirac equation. At the same
time it is shown that these sedeonic equations differ in space-time properties
and describe several types of massive and corresponding massless particles. In
particular we proposed four different equations, which could describe four
types of neutrinos.
